tests: update to reflect the mirror edit plane and the current mirror configuration

newMirror doesn't return an object anymore since it's only temporary. instead the state of newMirrors is tracked alongside the editingMirror map. once a mirror is saved, it's moved back to the mirrors list and removed from these lists. this must be reflected in tests

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
api update: delete should target by id in path and not just by query

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>