SLING-3286 - Remove plugin version overrides from poms

Remove most plugin version overrides. Still left in:

- a couple of projects where upgrading to the maven-bundle-plugins
  leads to errors (TODOs added)
- a couple of projects where the plugin version is newer than the
  one from the parent project ( comments added )

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1551060 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index fb59473..0813f91 100644
--- a/pom.xml
+++ b/pom.xml
@@ -82,7 +82,6 @@
         <plugins>
             <plugin>
                 <artifactId>maven-clean-plugin</artifactId>
-                <version>2.2</version>
                 <configuration>
                     <filesets>
                         <fileset>
@@ -90,7 +89,7 @@
                             <includes>
                                 <include>derby.log</include>
                                 <include>cachedir</include>
-                                <include>sling</include>
+                                <include>sling/**</include>
                                 <include>jackrabbit</include>
                                 <include>coverage.ec</include>
                             </includes>
@@ -220,6 +219,7 @@
                 <plugins>
                     <plugin>
                         <artifactId>maven-failsafe-plugin</artifactId>
+                        <!-- Version newer than the one declared in the parent pom -->
                         <version>2.16</version>
                         <executions>
                             <execution>