Functional tests spend too much time creating the DB

[John Bresnahan]

Every functional test in glance that creates a registry service and/or a api service also creates a fresh sqlite db by forking out a call to glance-manage db_sync. This is expensive now, and will only get more expensive, because db_sync must walk every migration.

We should change that a clean db is only created once and then cached. A copy of the cache could then be used for each test. An initial proof of concept shows that this could speed up tests by 3x

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/27450

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/27450
Committed: http://github.com/openstack/glance/commit/d41561151c7bd4917a36382340d040ed843a794b
Submitter: Jenkins
Branch: master

commit d41561151c7bd4917a36382340d040ed843a794b
Author: John Bresnahan <email address hidden>
Date: Wed Apr 24 11:35:24 2013 -1000

    Functional tests use a clean cached db that is only created once.

    This eliminates the need for 'glance-manage db_sync' to be called
    once (and often twice) for every test. db_sync is an expensive
    operation because it must walk through ever database migration.
    With this patch, the first time the db is created it is cached
    before it is used. Instead of creating the db in future tests
    the cached file is copied. An atexit() function is used to clean
    up the file when the tests are complete.

    fixes bug: 1172475
    blueprint: refactoring-better-faster-stronger-functional-tests

    Change-Id: I96e35c640256bf27ff17da0b5f558bda02906a07