combination alarm should be evaluatored by dependency order

[ZhiQiang Fan]

currently, the GET /alarms returns alarms ordered by id, but think about a complex scenarion, such as

create threshold alarm ta1
create threshold alarm ta2
create threshold alarm ta3
create combination alarm ca1, alarm_ids = ta1 and ta2
create combination alarm ca2, alarm_ids = ta1 or ta2
create combination alarm ca3, alarm_ids = ca1 and ta3

then alarm-evaluator get a list of alarms and evaluator them one by one, the order can be ca3, ca2, ca1, ta3, ta2, ta1
so ta1 and ta2 are properly updated in period 1
then ca1 and ca2 are properly updated in period 2
then ca3 is properly updated in period 3, then user get notified after 2 periods

the longer dependency chain is, the later user will get notified

I think we could update all alarms in one single period, which means if
ta1 and ta2 and ta3 are all triggerd, then ca3 should be triggerd in
same period.

I have another bug reported to solve dead loop in dependency chain, so in this bug fix, the cycled alarms may be ignored directly, this can be discussed in patch review

[ZhiQiang Fan (aji-zqfan)]

when write test code, I find that there is no guarantee for evaluate all alarms in one periods,

that because, even we can decide the right order when evaluate alarms, but the for loop is very quick and the evaluate process is very slow compare to the loop, so, there is a high possibility that the depended alarm is being evaluated and the state value is not flushed into database, the meanwhile, the alarm get request has been sent, so we get the state of last period of that alarm

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: master
Review: https://review.openstack.org/89330

[ZhiQiang Fan (aji-zqfan)]

after a deep thought, I think currently alarm-evaluator only has one work, and everything works in sequence, which means it is safe, my previous comment only valid in parallel or asychronous scenarions

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: stable/havana
Review: https://review.openstack.org/89335

[OpenStack Infra (hudson-openstack)]

Change abandoned by gordon chung (<email address hidden>) on branch: master
Review: https://review.openstack.org/89330
Reason: marking abandoned as this is crazy old. please reopen if you feel like it's still worthwhile.

[ZhiQiang Fan (aji-zqfan)]

@gordon I think we can remove the tag for Ceilometer because alarm code is going to be removed in this project.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/228154

[OpenStack Infra (hudson-openstack)]

Change abandoned by ZhiQiang Fan (<email address hidden>) on branch: master
Review: https://review.openstack.org/228154
Reason: too old