An ImageUpdateAutomation refers to a git repository and may refer to
an image policy. Watch both of these kinds, and react to either
changing by queueing any automations that refer to them.
This factors out the function that checks directories for equivalence,
and uses it to check that the upstream repo has the expected update
when the controller has pushed its commit.
This adds a test for the controller, checking that it will commit and
push a change, with the given commit message. I think checking it made
the right change will need a bit of rejigging tests elsewhere, so I
can compare directory contents (as with pkg/update tests).
Michael Bridgen