don't propagate InvalidPathException

[elharo]

@loosebazooka @lesv Likely not yet a full solution, but this is the first change we need to make for #427

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[elharo]

Results :

Tests run: 211, Failures: 0, Errors: 0, Skipped: 1

I'm not sure why the builds are failing.

[elharo]

On kokoro I do get an error:

Results :

Tests in error:
testValidateAppEngineJavaComponents(com.google.cloud.tools.appengine.cloudsdk.CloudSdkTest): Validation Error: Java App Engine components not installed. Fix by running 'gcloud components install app-engine-java' on command-line.

Tests run: 211, Failures: 0, Errors: 1, Skipped: 1