Add support for SSH-style git repo addresses (#835)

This allows nodes to be pulled from git repositories that:
1. Require authentication
2. Are located on a computer that does not have any special software
   beyond an SSH server to serve up git repos
3. Are hosted on sites that exclusively allow SSH access

I have also cleaned up the JavaScript regex for identifying valid HTTP
addresses. Due to an unescaped '.' and the lack of a count on the first
group, it wasn't doing a whole lot anyway -- just checking that the very
first character wasn't invalid.

glob/manager_core.py

@@ -515,10 +515,16 @@ class GitProgress(RemoteProgress):
 
 def is_valid_url(url):
     try:
+        # Check for HTTP/HTTPS URL format
         result = urlparse(url)
-        return all([result.scheme, result.netloc])
-    except ValueError:
-        return False
+        if all([result.scheme, result.netloc]):
+            return True
+    finally:
+        # Check for SSH git URL format
+        pattern = re.compile(r"^(.+@|ssh:\/\/).+:.+$")
+        if pattern.match(url):
+            return True
+    return False
 
 
 def gitclone_install(files, instant_execution=False, msg_prefix=''):