Allow single-label hostnames as a Host target (#126)

The target ("ip") field validator required at least two dot-separated
labels, rejecting legitimate single-label hostnames like Docker Compose
service names ("sso-manager"), /etc/hosts entries, or anything resolved
via a search domain. This was enforced identically client-side
(public/lib/js/val.js) and server-side (utils/hostname_validate.js,
routes/host.js), so there was no way to set one through the UI or API
— only by writing to the Host model directly, bypassing validation
entirely (which is how theta-env's setup.sh registers sso-manager as a
target today, working only because it calls Host.create() directly).

Relax HOSTNAME in both places to accept either a bare single label or
the existing dotted-FQDN pattern. Flips the one existing test that
codified the old behavior (isValidHostname('localhost') was asserted
false) and adds coverage for the reported case.

nodejs/public/lib/js/val.js

@@ -98,7 +98,9 @@
 // incoming host may be a wildcard ("*.example.com"); the target may not.
 (function(){
 	var LABEL = /^[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?$/i;
-	var HOSTNAME = /^(?=.{1,253}$)(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z]{2,63}$/i;
+	// Either one bare label (Docker service names, /etc/hosts entries) or a
+	// dotted hostname with an alphabetic TLD.
+	var HOSTNAME = /^(?=.{1,253}$)(?:(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z]{2,63}|[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?)$/i;
 	var FORBIDDEN = /[\s/:]/;
 
 	function isIPv4( value ) {