Protect against concurrent image uploads by allowing the
initial request to proceed and succeed and subsequent
concurrent requests to fail.
We now allow the upload activation to specify what state
it expects to transition to 'active' from. If by the time
the db is updated the transition has already occured i.e.
another upload has succeeded, the upload will fail and data
will be cleaned up.
Fixes: bug 1241025
Change-Id: Ie532b61484bec660910fb9a37429397bde8ef11f
51ecc8016a