1. There is no exception called `InvalidRollback` in Deckhand (it
was removed a while back). Instead, the only exception that
db_api.revision_rollback raises is RevisionNotFound from
the revision_get call internally.
So catch that instead from the controller.
2. The default value of parameters is `str` so when revision_id
of '0' is passed to the db module for processing, it skips over
the check for `if revision_id == 0` as revision_id is a str,
not int. So this leverages builtin int converter logic in
falcon [0] but requires uplifting the version of falcon to
at least 1.3.0 to make use of it [1].
[0] https://falcon.readthedocs.io/en/stable/api/routing.html#field-converters
[1] https://falcon.readthedocs.io/en/1.3.0/api/routing.html#field-converters
Change-Id: I068cd9e9b6818a5d51501f2718ee2d40d556c094
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