Add missing example snippet for incremental backups

[Robert Myers]

The example generator was recently merged without an example for incremental backups. Also the example generator has a assert statement commented out which makes it always pass instead of checking the api for validity.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/138142

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/138142
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=0a601ae45c7a7431572ed4bf2155732d1344aba7
Submitter: Jenkins
Branch: master

commit 0a601ae45c7a7431572ed4bf2155732d1344aba7
Author: Robert Myers <email address hidden>
Date: Mon Dec 1 12:23:31 2014 -0600

    Add missing api example for incremental backups

    * Added Incremental backup test and resulting sample files.
    * Fixed the example generator tests to actually fail when api
      changes.
    * Added changes since the last example generation was run.
    * Added a --fix-examples flag to the example generator to
      automatically correct the sample files.

    Change-Id: I7ac355c80b251b0eccd3bd5b8d76d2287c255705
    Closes-Bug: #1398119