vcs: make the not initialiazed exception more meaningfull.

rhodecode/lib/vcs/connection.py

@@ -25,7 +25,9 b' Holds connection for remote server.'
 
 def _not_initialized(*args, **kwargs):
     """Placeholder for objects which have to be initialized first."""
-    raise Exception("rhodecode.lib.vcs is not yet initialized")
+    raise Exception(
+        "rhodecode.lib.vcs is not yet initialized. "
+        "Make sure `vcs.server` is enabled in your configuration.")
 
 # TODO: figure out a nice default value for these things
 Git = _not_initialized