Wait for the server before validate the rotation result

This commit is for test:
tempest.api.compute.servers.test_server_actions:\
ServerActionsTestJSON.test_create_backup
In most cases, the nova service sends the response of
the request that queries the backups before the rotation
function completes its work, and then 3 backups will be
and the test will fail.
This commit makes the use case wait for the server to
become active before sends the query request to ensure
rotation task has completed before the verification.

Closes-Bug: #1257614

Change-Id: Ic6443e3835fdb9d53f5ab643a04312c59ecb4c58
Merge "Wait for the server before validate the rotation result"