mitaka: charmhelpers.contrib.openstack.utils.get_os_version_codename_swift returns 2.7.0

[Vultaire]

This was discovered as a potential but perhaps less likely issue. I have not encountered a problem with this code in the wild, but noted this during a different code review.

For charm-swift-storage units out in the wild, if any of them are running swift 2.7.0, the openstack_upgrade_available function of charmhelpers will likely not report the availability of swift 2.7.1.

Per the current trunk of charmhelpers:

>>> from charmhelpers.contrib.openstack import utils
>>> utils.get_os_version_codename_swift('mitaka')
'2.7.0'

The fix would simply be to stick a 2.7.1 in the SWIFT_CODENAMES data structure under "mitaka".

Again, this is being posted as a potential issue, not as a sighting of an in-the-wild problem. Newly-installed mitaka units pulling from trusty-updates/mitaka/main on the Ubuntu Cloud Archive would likely pull 2.7.1, bypassing this issue. I think this would only affect existing units running 2.7.0, for which openstack_upgrade_available() would not report a new version being available.