alarm-list filter by timestamp

[gordon chung]

taken from https://review.openstack.org/#/c/309887
==================================
Support Filter Alarms By Timestamp
==================================

https://blueprints.launchpad.net/aodh/+spec/place-holder
https://blueprints.launchpad.net/python-aodhclient/+spec/place-holder

Problem description
===================

Event alarm has been supported by Aodh, to improve the performance, it uses
ttl to cache alarms. However, ttl should not be very large, at least should
large than 1 minute comparing to threshold alarm, because event alarm aims
to provide real time alarming service.

Meanwhile, if ttl is small, then we will retrieve all enabled event alarms
when ttl exipres. In a middle or large scale deployment, it is a burden for
Aodh API and decrease the response time for event alarm.

Proposed change
===============

Here I proposal a change that enable us to retrieve alarms filtered by their
last update time, named "timstamp", so event evaluator can only get alarms
from last ttl expire time.

To allow such functionality, here are what we need to do:

* update timestamp when we call , currently we only update
  the state_timestamp field, it is wrong actually
* provide storage level support for such feature
* provide API level support for such feature
* provide CLI level support for such feature

Alternatives
------------

Let event evaluator suffer.

Data model impact
-----------------

None

REST API impact
---------------

New parameter provided, but user can ignore it if they don't interest.

Security impact
---------------

None

Pipeline impact
---------------

None

Other end user impact
---------------------

None

Performance/Scalability Impacts
-------------------------------

Yes, aodh-listener and aodh-api will be happy.

Other deployer impact
---------------------

None

Developer impact
----------------

None, or they have more code to maintain?

Implementation
==============

Assignee(s)
-----------

Primary assignee:
  <zqfan>

Other contributors:
  <None>

Ongoing maintainer:
  <zqfan>

Work Items
----------

See the above section.

Future lifecycle
================

More attribute can be filtered, provide more sensitive API user experience.

Dependencies
============

None

Testing
=======

Unit test and API test will be provide along with code.

Documentation Impact
====================

Yes, we need to update our document for such feature.

References
==========

None