validation for NFS URI (bug #1170700)

Added NFS uri validation for cinder and glance.

https://bugzilla.redhat.com/show_bug.cgi?id=1170700

Validates format of <server IP or hostname/fqdn>:<local path>

The first element must be an IP address or valid hostname/fqdn.
For the local path element, the only validation is that it's
not empty.
The reason I"m using '&lt;server&gt;:&lt;local path&gt;' there is that I tried it first as <server>:<local path>' and all I saw in the UI was ":" since the <foo> bits were swallowed as html tags. With the &lt;, etc. I saw the error message as I expected. If you have a chance to test this out on Monday, lets see if you see the same thing I guess.