guest_log_long_query_time should be controlled via configuration groups

[Petr Malik]

Datastores that support slow query logging should allow the 'long query time' be configured via the existing configuration group mechanism.

The 'long query time' is a database configuration option and as such should be managed like other options via configuration groups.

The value is currently retrieved from Trove config which can be only changed globally by the cloud operator.
Any changes applied by end-users via configuration groups will be 'silently' overriden by this global configuration value.

The configuration group mechanism would allow users set whatever time is appropriate for their particular application.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/311237

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/311237
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=665bdaefc13f3e91a3db557d615b4b96eed3b47c
Submitter: Jenkins
Branch: master

commit 665bdaefc13f3e91a3db557d615b4b96eed3b47c
Author: Petr Malik <email address hidden>
Date: Fri Apr 29 15:34:51 2016 -0400

    Deprecate 'guest_log_long_query_time'

    Slow query time should be configurable on per-instance basis
    via the existing configuration group mechanism (see the bug).

    We need to deprecate the existing global conf property first.
    The property has been deprecated on all datastores.

    Validation rules have been updated on those that
    support log retrieval as well:

      - MySQL: long_query_time
      - Percona: long_query_time
      - Percona XtraDB Cluster: long_query_time
      - PostgreSQL: log_min_duration_statement
      - MariaDB: long_query_time

    The logging settings will be saved with lower 'priority' than
    any user settings. This will ensure the user settings
    (if present) always override the global value.
    Once the deprecated options go away we can again apply
    the logging settings at the system level.

    Change-Id: I9c28ceb933b6819b8e96556584b2e26cab2155fb
    DocImpact: Document deprecated properties
    Partial-Bug: 1542485