When running a rolling upgrade, each swift node is addressed
individually. This can result in undefined variables when a node doesn't
have the necessary SSH and ring information.
For minor upgrades, these changes are not necessary. They are only
necessary in fresh installs, or modifying storage capacity. Thus, this
patch checks to see if it's a new install (no swift venv_tag previously
defined) or it's the same version (current venv tag matches the previous
one) and only does syncs in those cases.
Change-Id: Ice3b4526609f5a5fd4472c8408de9ed08aea29e6