Previously: replace the YNode (yaml.Node) with a new one which is just
the replacement string.
Now: change the value of the YNode, and set it back in place.
When I set my default branch for `git init` in ~/.gitconfig, tests
start failing. This is because go-git assumes a default of `master`
when e.g., pulling commits, but exec'ing git (as the test server does,
via gitkit) will get you a different branch.
The answer is to be explicit about the branch created in tests, and in
all operations like cloning. The natural end point is that the
automation object specifies a branch to use (or an empty value,
meaning let it default).
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.
Michael Bridgen