Fix a potential race condition, the member batch update API call
computes a delta between the current state of the members in the DB and
the members in the requests. But it fetches the members from the DB
before locking the load balancer, it means that another Octavia service
may still update the list of members, then the computation of the
changes may be incorrect.
The list of members is now queried in the locked section.
Closes-Bug: #2036156
Change-Id: I453ff385620f488a3e43d4fda01634cdce3be5d4
(cherry picked from commit 8a47577b7668e6dc82e048d937d1344c667e5124)
(cherry picked from commit 8a5bed4cebd70c1c721a3916dc79f2b19343e445)
64d9bdb975