Alarms listing based on "timestamp"

Fixes are proposed for ordering alarms based
on "timestamp" in descending order.
Existing tests has been modified at storage
and api without breaking their functionality.

One test case has been provided with this patch.

Co-Authored-By: Ilya Tyaptin <ityaptin@mirantis.com>

Change-Id: Ie2bb950b6d32188f451f905e2cf07e4d938df1ac
Closes-Bug: #1287119
Merge "Alarms listing based on "timestamp""