Move wait_for_qos_operations method to common.waiters

Currently, wait_for_qos_operations method resides on
BaseVolumeAdminTest class. I think we should move it
to common.waiters module as other waiters functions.

Partially implements blueprint consistent-service-method-names

Change-Id: Ia687451e4fddfc1408c2570697068415c1124c38
3 files changed