This allows us to construct a job which allows users to pass in a
secret (via pass-to-parent) which includes not only the user/pass,
but also a restriction for what docker image repositories may be
accessed using that user/pass. This allows an operator to create
one credential, and then use that credential in multiple secrets
for multiple projects, each with a distinct restriction on where
images may be uploaded.
Change-Id: I7a3cf97a16d34c76df8601990954e1f2b0e498f5
3e3f836435