Slave provisioning failing when trying to create a "slave of a slave"

[Denis M.]

Replication V1 should allow only flat hierarchy - one root replica
  with multiple read replicas. Trove should forbid attempts to create
  slave of slave of slave and so on.

Bug described at: https://review.openstack.org/#/c/98147/23/trove/instance/models.py,cm

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/117298

[OpenStack Infra (hudson-openstack)]

Change abandoned by Denis M. (<email address hidden>) on branch: master
Review: https://review.openstack.org/117298

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/119771

[OpenStack Infra (hudson-openstack)]

Change abandoned by iccha-sethi (<email address hidden>) on branch: master
Review: https://review.openstack.org/117298

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/119771
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=a91c9d32051c504b6d2321050b89e710b3649d0b
Submitter: Jenkins
Branch: master

commit a91c9d32051c504b6d2321050b89e710b3649d0b
Author: Denis Makogon <email address hidden>
Date: Mon Sep 8 16:58:21 2014 +0300

    Forbid replica provisioning from replica site

    Reasons:
    - Replication V1 should allow only flat hierarchy - one root replica
      with multiple read replicas. Trove should forbid attempts to create
      slave of slave of slave and so on.

    Changes:
     - adding validation step that forbids read replica provisioning if passed
       replica source (slave_if_id) is not an actual source (is a read replica any
       other replica source)
     - unit test added

    Co-Authored-By: Iccha Sethi <email address hidden>

    Change-Id: Ic467b2eb01194f95a30f7ce9d921d3fa942b086e
    Closes-Bug: #1357707