Update BrooklynMavenArtifactsTest.java

Updated snapshot and release check. Updated checkValidArchive to test for the release path.

Test passed here: [brooklyn.builds.cloudsoftcorp.com/...brooklyn.util/BrooklynMavenArtifactsTest/testHistoricHosted](http://brooklyn.builds.cloudsoftcorp.com/job/Brooklyn-Master-Integration-testhistorichostedfix/io.brooklyn$brooklyn-core/3/testReport/brooklyn.util/BrooklynMavenArtifactsTest/testHistoricHosted/)