rationalize trove configuration with respect to datastore specific options for incremental backup

[Amrith Kumar]

Currently, while backup strategy is datastore specific, it appears that incremental backup strategy is a common option.

This may have been OK when all data stores looked like MySQL. That's not the case any longer.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/113155

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/113155
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=ca33edd44b2a1dd916bba2141f35edf20b2e36a0
Submitter: Jenkins
Branch: master

commit ca33edd44b2a1dd916bba2141f35edf20b2e36a0
Author: Amrith Kumar <email address hidden>
Date: Sun Aug 10 12:57:26 2014 -0400

    make backup_incremental_strategy a datastore specific option

    backup_incremental_strategy remained a common option even after
    backup_strategy became a datastore specific option. This change moves
    backup_incremental_strategy to a datastore specific option with the
    appropriate decorations for deprecation.

    Change-Id: I6113ae9aede6b2c9cb960320e05960df2de34566
    Closes-Bug: #1354959