Only add mentoring application to INSTALLED_APPS when in virtualenv

lms/envs/common.py

@@ -26,6 +26,7 @@ Longer TODO:
 
 import sys
 import os
+import imp
 import json
 
 from path import path
@@ -1163,9 +1164,6 @@ INSTALLED_APPS = (
     'reverification',
 
     'embargo',
-
-    # XBlocks containing migrations
-    'mentoring',
 )
 
 ######################### MARKETING SITE ###############################
@@ -1458,11 +1456,22 @@ ALL_LANGUAGES = (
 )
 
 
-### JSdraw (only installed in some instances)
+### Apps only installed in some instances
 
-try:
-    import edx_jsdraw
-except ImportError:
-    pass
-else:
-    INSTALLED_APPS += ('edx_jsdraw',)
+OPTIONAL_APPS = (
+    'edx_jsdraw',
+    'mentoring',
+)
+
+for app_name in OPTIONAL_APPS:
+    # First attempt to only find the module rather than actually importing it,
+    # to avoid circular references - only try to import if it can't be found
+    # by find_module, which doesn't work with import hooks
+    try:
+        imp.find_module(app_name)
+    except ImportError:
+        try:
+            __import__(app_name)
+        except ImportError:
+            continue
+    INSTALLED_APPS += (app_name,)