Make auto service optional

This makes dependencies consistent and eliminates warnings of the
form:

$M2_HOME/repository/org/apache/jclouds/driver/jclouds-slf4j/2.1.0-SNAPSHOT/jclouds-slf4j-2.1.0-SNAPSHOT.jar(org/jclouds/logging/slf4j/config/SLF4JLoggingModule.class): warning: Cannot find annotation method 'value()' in type 'AutoService': class file for com.google.auto.service.AutoService not found

Reference:

https://github.com/google/auto/tree/master/service#download
diff --git a/openstack-glance/pom.xml b/openstack-glance/pom.xml
index 80759ac..67ebcab 100644
--- a/openstack-glance/pom.xml
+++ b/openstack-glance/pom.xml
@@ -101,6 +101,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/openstack-heat/pom.xml b/openstack-heat/pom.xml
index eb53851..3de77b5 100644
--- a/openstack-heat/pom.xml
+++ b/openstack-heat/pom.xml
@@ -99,6 +99,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
     <dependency>
       <groupId>com.google.auto.value</groupId>
diff --git a/openstack-marconi/pom.xml b/openstack-marconi/pom.xml
index 40863d6..0161286 100644
--- a/openstack-marconi/pom.xml
+++ b/openstack-marconi/pom.xml
@@ -104,6 +104,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/openstack-neutron/pom.xml b/openstack-neutron/pom.xml
index eff1d88..1446d98 100644
--- a/openstack-neutron/pom.xml
+++ b/openstack-neutron/pom.xml
@@ -110,6 +110,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
     <dependency>
       <groupId>com.google.auto.value</groupId>
diff --git a/openstack-poppy/pom.xml b/openstack-poppy/pom.xml
index af55c7b..c74c483 100644
--- a/openstack-poppy/pom.xml
+++ b/openstack-poppy/pom.xml
@@ -86,6 +86,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
     <dependency>
       <groupId>com.google.auto.value</groupId>
diff --git a/rackspace-autoscale-uk/pom.xml b/rackspace-autoscale-uk/pom.xml
index c94a63c..0a6a9bb 100644
--- a/rackspace-autoscale-uk/pom.xml
+++ b/rackspace-autoscale-uk/pom.xml
@@ -118,6 +118,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-autoscale-us/pom.xml b/rackspace-autoscale-us/pom.xml
index 2b61576..34286c5 100644
--- a/rackspace-autoscale-us/pom.xml
+++ b/rackspace-autoscale-us/pom.xml
@@ -117,6 +117,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-autoscale/pom.xml b/rackspace-autoscale/pom.xml
index 0e1e541..49618c8 100644
--- a/rackspace-autoscale/pom.xml
+++ b/rackspace-autoscale/pom.xml
@@ -110,6 +110,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-cloudbigdata-us/pom.xml b/rackspace-cloudbigdata-us/pom.xml
index 9178725..928e2af 100644
--- a/rackspace-cloudbigdata-us/pom.xml
+++ b/rackspace-cloudbigdata-us/pom.xml
@@ -122,6 +122,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-cloudbigdata/pom.xml b/rackspace-cloudbigdata/pom.xml
index 362fd25..487754e 100644
--- a/rackspace-cloudbigdata/pom.xml
+++ b/rackspace-cloudbigdata/pom.xml
@@ -115,6 +115,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-cloudnetworks-us/pom.xml b/rackspace-cloudnetworks-us/pom.xml
index 385118f..aeb8a3c 100644
--- a/rackspace-cloudnetworks-us/pom.xml
+++ b/rackspace-cloudnetworks-us/pom.xml
@@ -87,6 +87,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-cloudqueues-uk/pom.xml b/rackspace-cloudqueues-uk/pom.xml
index 7bf2252..fd962f9 100644
--- a/rackspace-cloudqueues-uk/pom.xml
+++ b/rackspace-cloudqueues-uk/pom.xml
@@ -123,6 +123,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 
diff --git a/rackspace-cloudqueues-us/pom.xml b/rackspace-cloudqueues-us/pom.xml
index 0e0aa19..89074f5 100644
--- a/rackspace-cloudqueues-us/pom.xml
+++ b/rackspace-cloudqueues-us/pom.xml
@@ -123,6 +123,7 @@
       <groupId>com.google.auto.service</groupId>
       <artifactId>auto-service</artifactId>
       <scope>provided</scope>
+      <optional>true</optional>
     </dependency>
   </dependencies>