Allow repotest OCI server to bind to localhost

[brucec5]

What this PR does / why we need it:

This adds a repotest.NewOCIServerWithBindAddress function for building an OCI server that binds to a specific address, eg.

ociServer, err := repotest.NewOCIServerWithBindAddress(t, repoDir, "localhost")

The current repotest.NewOCIServer function binds to an empty address, which means binding to all interfaces. This gets annoying when locally running tests that use repotest, as the Macos firewall dialog box will pop up every time you run tests.

I figured it would technically be backwards incompatible to just change repotest.NewOCIServer to bind to localhost instead of all interfaces, so I decided to split that out into a separate function. I assume most people probably don't rely on exposing the repotest server outside localhost (especially since the returned RegistryURL is for localhost), but someone could conceivably be depending on that.

Special notes for your reviewer:

I didn't see any test coverage for this function, so I'll probably need to write that if you think this change is a good idea.

If applicable:

• this PR contains documentation
• this PR contains unit tests
• this PR has been tested for backwards compatibility