Provide better error message for aggregate-create

For an InvalidAggregateAction exception:
Before: 'ERROR: There was a conflict when trying to complete your request (HTTP 409)'
After: 'ERROR: Cannot perform action 'create_aggregate' on aggregate 'N/A'. Reason: invalid zone. (HTTP 400)'

docImpact

Fix bug 1083353

Change-Id: I26e30059fe5bbc30eecc52cccec4eba2a57d00db
(cherry picked from commit 4e43747037058522087e6eb71ef3bcce266d55cc)
Merge "Provide better error message for aggregate-create" into stable/folsom