Fix hostname validation for nameservers

Fixes the hostname validation to align with the RFC's demands[1].
This was done by replacing the full regex with a function that
broke the FQDN into individual components that were easier to
reason about with regular expressions.

Also added several test cases for domains so if someone wants
to convert it back to pure regex there will be better test vectors.

1. RFC 1123 says an all-digit hostname is allowed in section 2.1. It
   says that this more liberal syntax MUST be supported.

Closes-Bug: #1396932
Change-Id: I003cf14d95070707e43e40d55da62e11a28dfa4e
Update i18n translation for Midonet plugin

All the existing LOG.info, LOG.warning, LOG.error and LOG.critical
messages should have _LI, _LW, _LE and _LC respectively. Also, debug
level log shouldn't be translated. This patch set will cover the midonet
directory.

Change-Id: Ic74316640015bc98ec4b2722f4039f58a9ec2379
Partial-Bug: #1320867
Merge "Update i18n translation for Midonet plugin"
Merge "Fix hostname validation for nameservers"