Pool Manager doesn't retry Creates/Deletes

[Tim Simmons]

When a Create/Delete fails in the Pool Manager for any reason (rndc failure, unavailable pdns database, network split) on a target, the code does not retry, and immediately triggers an ERROR state.

```
         try:
            backend.create_domain(context, domain)

            return True
        except Exception:
            LOG.exception(_LE("Failed to create domain %(domain)s on target "
                              "%(target)s"),
                          {'domain': domain.name, 'target': target.id})
            return False
```

This is different behavior than an update, and should be the same, because many times, a Create/Delete will succeed on the second try.

[Kiall Mac Innes (kiall)]

https://review.openstack.org/#/c/230767/2

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/230767
Committed: https://git.openstack.org/cgit/openstack/designate/commit/?id=94dfad359f021ac3a15b2f7900611cc8425827d3
Submitter: Jenkins
Branch: master

commit 94dfad359f021ac3a15b2f7900611cc8425827d3
Author: TimSimmons <email address hidden>
Date: Sat Oct 3 13:32:09 2015 -0500

    retry creates/deletes in the pool manager

    - The pool manager doesn't retry creates/deletes right away. If there's
    just a small net split, or the DNS server has some temporary failure, trying
    a second time will usually succeed. This should fix a lot of premature ERROR
    states

    Change-Id: Ib61110c4e460e93b8b5cfa8a9256151a5cabc43b
    closes-bug: #1503350