Exclude Compile-Testing's circular dependency on Truth.

Maven already largely ignores this, but the circularity does cause Maven a couple problems:

- It causes errors under dependencyConvergence (which I'm not 100% sure we want to turn on but which I've been experimenting with).
- It makes Maven print out the dependency tree in a confusing way, with Truth listed as if it were a direct dependency of itself (rather than a dependency through Compile-Testing) and Compile-Testing's other dependencies missing entirely.

Here's the diff in Maven's dependency:tree output produced by this change:

$ ( filter() { grep -v -e SUCCESS -e Downloaded -e 'Total time' -e 'Finished at' $@; }; diff <(filter /tmp/pre) <(filter /tmp/post) )
--- /dev/fd/63  2018-08-14 13:58:21.938426152 -0400
+++ /dev/fd/62  2018-08-14 13:58:21.942426128 -0400
@@ -68,9 +68,13 @@
 [INFO] |  +- (com.google.j2objc:j2objc-annotations:jar:1.1:test - omitted for duplicate)
 [INFO] |  +- (com.google.guava:guava:jar:25.1-android:test - version managed from 25.1-jre; omitted for duplicate)
 [INFO] |  \- (junit:junit:jar:4.12:test - version managed from 4.11; omitted for duplicate)
-[INFO] +- (com.google.truth:truth:jar:0.37:test - omitted for cycle)
 [INFO] +- com.google.testing.compile:compile-testing:jar:0.15:test
-[INFO] |  \- (junit:junit:jar:4.12:test - version managed from 4.11; omitted for duplicate)
+[INFO] |  +- (junit:junit:jar:4.12:test - version managed from 4.11; omitted for duplicate)
+[INFO] |  +- (com.google.guava:guava:jar:25.1-android:test - version managed from 23.5-jre; omitted for duplicate)
+[INFO] |  +- (com.google.auto.value:auto-value:jar:1.6.2:test - version managed from 1.5.3; omitted for duplicate)
+[INFO] |  +- com.google.auto:auto-common:jar:0.9:test
+[INFO] |  |  \- (com.google.guava:guava:jar:25.1-android:test - version managed from 23.5-jre; omitted for duplicate)
+[INFO] |  \- com.sun:tools:jar:1.8.0_151-google-v7:system
 [INFO] \- com.google.errorprone:error_prone_annotations:jar:2.3.1:compile
 [INFO]
 [INFO] ------------------------------------------------------------------------

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=208682723

pom.xml

@@ -92,6 +92,17 @@
         <groupId>com.google.testing.compile</groupId>
         <artifactId>compile-testing</artifactId>
         <version>0.15</version>
+        <exclusions>
+          <exclusion>
+            <groupId>com.google.truth</groupId>
+            <artifactId>truth</artifactId>
+          </exclusion>
+          <!-- TODO(cpovirk): Remove after a Compile-Testing release moves this test scope. -->
+          <exclusion>
+            <groupId>com.google.truth.extensions</groupId>
+            <artifactId>truth-java8-extension</artifactId>
+          </exclusion>
+        </exclusions>
       </dependency>
       <dependency>
         <groupId>com.google.errorprone</groupId>
@@ -273,11 +284,11 @@
         </plugin>
       </plugins>
     </pluginManagement>
-    <!--
-      Force a version >2.7 for this parent project. If we use the current
-      default of 2.7, Maven ignores this parent project's configuration when
-      running maven-javadoc-plugin in children during releases.
-      -->
+      <!--
+        Force a version >2.7 for this parent project. If we use the current
+        default of 2.7, Maven ignores this parent project's configuration when
+        running maven-javadoc-plugin in children during releases.
+        -->
     <plugins>
       <plugin>
         <artifactId>maven-javadoc-plugin</artifactId>