Fix is_hostname_safe for RFC compliance

[Michael Davies]

In review https://review.openstack.org/#/c/165443 we added the ability to specify a FQDN for a node's logical name.

Unfortunately the implementation missed a couple of other changes that would allow a hostname to be used as the Node's logical name. Specifically:

1) Change to a maximum of 255 chars
2) Allowing each hostname or domain name in the FQDN to be up to 63 chars
3) Differentiating between hostname, and domain name (different regexs required)
4) Allowing _ in the domain names
5) Allowing . at the end of a FQDN

Also added tests for the above rules.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/165666

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/165666
Committed: https://git.openstack.org/cgit/openstack/ironic/commit/?id=2d71701a279964f70210b05f6095c84d0de91c56
Submitter: Jenkins
Branch: master

commit 2d71701a279964f70210b05f6095c84d0de91c56
Author: Michael Davies <email address hidden>
Date: Wed Mar 18 17:37:26 2015 -0700

    Fix is_hostname_safe for RFC compliance

    In the move from Node name supporting just a hostname to now
    supporting a FQDN, we missed a few changes to keep this function
    being RFC compliant. This patch enhances the code and tests for
    this, and migrates the database to the longer name field format.

    Change-Id: Ib75c8b138d7165aedc74efead80d3fb755cab87b
    Closes-Bug: #1433832