Removed unnecessary lock from a aggregate test

Lock is unnecessary here, as the test is not adding
a host to an aggregate.Previoulsy this lock was
added to ensure the failure will not occur where
a host is added to an availability zone.
Reference:-
Iaf8a903d92c88c7c3092eaa00a9f7a96e6348ddc

Change-Id: I9d6d610302406d5aa7bee9135c27dbc83896e005
Merge "Removed unnecessary lock from a aggregate test"