Add test for synchronous replication

[rg2011]

This PR adds a new test for resource replication, based on client-go FakeDynamicClient to simulate a connection to an actual cluster. The test checks that kube-mgmt reads the resources in this fake cluster and pushes them to a mocked OPA data interface.

Unfortunately, FakeDynamicClient brings in a few new dependencies (github.com/pkg/errors, github.com/evanphx/json-patch) and vendors a few more libs. But I think it's worth adding the test, to address confidently some pending issues related to resource sync that I intend to fix (#11, #134)

To ease testing, I have modified data.New to accept the fake dynamic.Interface as a parameter, instead of a *rest.Config, which incidentally also fixes issue #99.

I have also refactored generateSyncPayload and objPath as functions instead of methods, and made sync.Run receive a context.Context instead of returning one quit chan struct{} per resource, for the sake of easier testing.

[srenatus]

Some nitpicks, but nothing that can't be ignored; just stylistic preferences.

I'm uncertain about the API compatibility; do you, or does anyone, have any insights into that...?

[srenatus]

Thanks a lot!

Something seems to be slightly odd with your committer email vs github account settings: github still thinks your a first-time contributor. Is that something you care about? Otherwise, this looks good to go.

[rg2011]

Thanks for pointing out. I've reviewed my github settings and pushed again with the proper user and email (I hope). Let's see if it makes a difference. Otherwise never mind, let's go with with this PR as it is and I'll try to figure out later.

[srenatus]

Thanks