This PS updates the Armada apply --set flag documentation to
be in line with the actual implementation. Each override
must be of the form:
manifest:simple-armada:release_name="wordpress"
Or:
manifest:simple-armada:chart_goups="foo","bar"
This PS also adds a few more unit tests for Override handler.
Change-Id: Ie280752ceee75a9a13d1ffafb40589c294407b46