Roll back reservations quota in RPC if necessary

Roll back reservations quota in RPC if necessary

Currently the latest version of the volume rpcapi passes along
old_reservations in retype whereas older versions do not. In the
case where old_reservations aren't passed, they will be checked again
in c-vol. This patch rolls back the quotas that were checked for
old_reservations if the client can't send the latest version in
the RPCAPI so that they aren't reserved twice.

This is an amendment to this recently merged patch:
Iba24edd8ad824837028353b52c90742df55c9173

Closes-Bug: 1546089
Related-bug: 1508249
Change-Id: I54b39f367b8552ed5e932c71265432e7cf72c073