add newly added constraints to expire clear_expired_metering_data

- cascade deletes to metadata tables on meter deletion
- delete associations on object deletion
- add check to not delete user/project entries associated with Alarm

Change-Id: I24cbaea9ede6d142dc22eaf070b3f7d1f14b484a
Closes-Bug: #1258071
doc: remove note about Nova plugin framework

The architecture doc alludes to a Nova plugin framework which is now
considered obsolete.

See oslo-incubator review I5552b5625e26f4821464807743545ec6f5117f2b
(commit 4b78868) for more background.

Change-Id: Id170510bc3147af94941c993ffe6997c418d4be4
config: specify a template for mktemp

It's actually not portable to use mktemp without an argument, so let's
add a default template.

Change-Id: I5c254b12c05457d9e3ed5788dabb4c317d97b4aa
Event Storage Layer

This change adds the storage layer interfaces
necessary to implement the Event API. It also
updates the get_events call to allow multiple
trait filters.

implements bp specify-event-api

Change-Id: I7aef4a8fc9b88528479f6c0a9feab2c18945bae3
service: fix service alive checking

This change the way we check for service being alive in a more portable
way by using os.kill() with a null signal.

Change-Id: I588ab19de15b351c1de3ab28b8655e400b2a2064
Merge "doc: remove note about Nova plugin framework"
Merge "config: specify a template for mktemp"
Merge "add newly added constraints to expire clear_expired_metering_data"
Merge "Event Storage Layer"
Merge "service: fix service alive checking"