Recognise arn: for REST stack lookup.

Note that the Routes mapper does brittle regexp fu to map parameters,
hence using \x3A for matching a colon

Fixes: Bug #1131759
Change-Id: I063bf9057782c1c0a3f809d4f8068e2594be264d
Delay calling _get_user() until AccessKey is created

Change-Id: I149909d9677f348edd415d3e5f37322b8ad33d28
Fixes: bug #1153397
Merge "Recognise arn: for REST stack lookup."
Merge "Delay calling _get_user() until AccessKey is created"