Fixes missing ec2 api address disassociate error on failure

Fixes ec2 api address disassociate so that the ec2 error
InvalidAssociationID.NotFound is returned when it is passed an
invalid association rather than returning success. Note this is
slightly different than the original bug report but the type
of failure has changed since the bug was originally filed.

Change-Id: I10034a2fed62d4e93bc384aef3ff594b66e285f2
Closes-Bug: 1179816
Merge "Fixes missing ec2 api address disassociate error on failure"