Update aggregate should not allow duplicated names

It is not allow to create 2 aggregates with the same name
but if update an existing one with a name already used
by other aggregate that check should be made.
This patch doesn't allow to change the name to an existing
one.

Change-Id: Icfe315594beaec94229e5a4a4c1bb80fc366b66e
Closes-Bug: #1288296
(cherry picked from commit 2b2decfd1b5b0d68813bc7e5b5e4349a1ab592aa)
Merge "Update aggregate should not allow duplicated names" into stable/havana