valid.FQDN should allow more cases

Previously, valid.FQDN rejected hostnames which are otherwise
allowed. Make sure that we allow hostnames which end with a raw
dot, have levels comprised of nothing but numbers, and other
edge cases.

For the time being, disallow entries which look like
IP addresses (\d+.\d+.\d+.\d+), but allow other variations on that
theme (RFC1123 technically allows this, and specifies that IP
addresses should be tried first with DNS second for the [surprisingly
valid] IPv4-identical FQDNs though RFC1738 implies that TLDs in URLs
will never start with a digit.

Updated doctests to match.

Change-Id: Iacbd4b5358143c0f1be5ed263ad2393283540d33
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=981614
Signed-off-by: Ryan Barry <rbarry@redhat.com>