Ignore empty machine addresses
mend
Merge pull request #136 from wallyworld/ignore-empty-machine-addresses

Ignore empty machine addresses

Older versions of juju could write empty machine addresses to state. This messes up the peer address selection when upgrading a nonha env to a ha one. So we add code to ignore such empty addresses.

Fixes: https://bugs.launchpad.net/juju-core/+bug/1329123