Make sure Travis passes for non-branch pull requests

[tswast]

I did pull out integration tests already for the cloud-vision repository (though more work is needed GoogleCloudPlatform/cloud-vision#50). It means that Travis can at least run the unit tests for pull requests from other repos, skipping the integration tests.

• Ignore decryption failure.
• Run build without the tests. `mvn verify -DskipTests=true
• Pull out integration tests (that need service account) and run all but those.

[tswast]

Example of failed build from external PR: https://travis-ci.org/GoogleCloudPlatform/java-docs-samples/builds/117868157

[lesv]

Obsolete.