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.

cm-cli.py

@@ -201,7 +201,7 @@ cm_ctx = Ctx()
 
 
 def install_node(node_name, is_all=False, cnt_msg=''):
-    if '://' in node_name:
+    if core.is_valid_url(node_name):
         # install via urls
         res = core.gitclone_install([node_name])
         if not res: