Code review comment for lp:~jjo/charms/trusty/mongodb/jjo-lp1274947-use_private-address_at_rs-initiate

Should cope with mongo rs.initiate() on hosts with 'invalid' hostname (see lp#1274947), I'm manually fixing them after deployment with: https://gist.github.com/jjo/198e27c8e44f68724fcd - this MP tries to implement that in-charm.