HV-1549 Use mvn install instead of mvn verify in the Travis build

'mvn verify' is theoretically the way to go, but in practice it leads to
some issues.
In particular, Maven plugins that need to retrieve artifacts (such as
those used to add our modules to the WildFly server) usually don't know
about the artifacts packaged during the current build, and they end up
looking for the required artifacts in the local Maven repository.
If we use 'mvn verify', the artifacts used for testing will then be
retrieved from a remote repository, and we'll end up executing WildFly
ITs against a nightly build...
Using 'mvn install' solves the issue by populating the local repository
with the version currently being built.

Also, this commit adds a 'before_cache' operation to avoid dirtying the
cache with the artifacts currently being built.

Author: yrodiere

.travis.yml

@@ -28,4 +28,7 @@ before_script:
 script:
   - ./mvnw $BUILD_OPTIONS -DskipDistro=true checkstyle:check
     && BUILD_OPTIONS+=' -Dcheckstyle.skip'
-    && ./mvnw $BUILD_OPTIONS clean verify
+    && ./mvnw $BUILD_OPTIONS clean install
+before_cache:
+  # Do not put Hibernate Validator artifacts into the cache
+  - rm -r $HOME/.m2/repository/org/hibernate/validator/ $HOME/.m2/repository/org/hibernate/hibernate-validator*