Add jobs to verify changes sent to infra/test repo

This change adds jobs to verify changes sent to infra/test repo in
order to ensure changes do not break things as infra/test repo will
be used for gating, post-merge and periodic jobs and have blocking
effect.

The job is expected to run on a slave with an existing deployment.
See the comments in cloud-infra-verify-test.yaml for details.

Change-Id: Ibe6271bbfd71c0a0d599964189f64619b582da45