Update tests.sh to locally install all Java packages, not just util

The JRuby test runs appear to be fetching the util package from Maven
Central because it is not being installed locally. This causes the tests
to fail when we upgrade to a new version that has not yet been published
to Maven Central. This commit fixes the problem by locally installing
all the protobuf packages, not just util.

tests.sh

@@ -226,7 +226,7 @@ internal_build_java() {
   cp -r java $dir
   cd $dir && $MVN clean
   # Skip tests here - callers will decide what tests they want to run
-  $MVN install -pl core -Dmaven.test.skip=true
+  $MVN install -Dmaven.test.skip=true
 }
 
 build_java() {