Make test execution more robust

- Execute tests hermetically where possible. This shields the tests from
weird interactions with the local network configuration.
- Run the integration tests in a fixed time zone. For some reason they
fail in Europe/London.
diff --git a/integration/pom.xml b/integration/pom.xml
index 07d55ca..7d7ce7e 100644
--- a/integration/pom.xml
+++ b/integration/pom.xml
@@ -1543,6 +1543,10 @@
                                 <java.awt.headless>true</java.awt.headless>
                                 <test.functional.ServicePort>${test.functional.ServicePort}</test.functional.ServicePort>
                             </systemPropertyVariables>
+                            <environmentVariables>
+                                <!-- TODO: some tests fail in specific time zones (e.g. Europe/London) -->
+                                <TZ>PST8PDT</TZ>
+                            </environmentVariables>
                         </configuration>
                     </execution>
                 </executions>
diff --git a/pom.xml b/pom.xml
index 08849eb..8b1e9df 100644
--- a/pom.xml
+++ b/pom.xml
@@ -422,6 +422,21 @@
                 <artifactId>maven-scm-publish-plugin</artifactId>
                 <version>1.0-beta-2</version>
             </plugin>
+            <plugin>
+                <groupId>com.github.veithen.maven</groupId>
+                <artifactId>hermetic-maven-plugin</artifactId>
+                <version>0.5.0</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>generate-policy</goal>
+                        </goals>
+                        <configuration>
+                            <allowCrossProjectAccess>true</allowCrossProjectAccess>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
     <profiles>
diff --git a/samples/transport-sample/pom.xml b/samples/transport-sample/pom.xml
index 2f91607..acb4de8 100644
--- a/samples/transport-sample/pom.xml
+++ b/samples/transport-sample/pom.xml
@@ -53,6 +53,14 @@
     <build>
         <plugins>
             <plugin>
+                <groupId>com.github.veithen.maven</groupId>
+                <artifactId>hermetic-maven-plugin</artifactId>
+                <configuration>
+                    <!-- TODO: the sample transport writes files to the project root directory -->
+                    <skip>true</skip>
+                </configuration>
+            </plugin>
+            <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
                 <executions>
                     <execution>