Fix hacking.py to handle 'cannot import x'

Fix missingImport logic to handle a module that cannot be imported, due
to a missing dependant module.

Due to the nature of this bug doctests cannot cover it.

Fix bug 1133103

Change-Id: Ia067bacc125b67e2d9e0cfc72495e4f13a8648ad

tools/hacking.py

@@ -201,7 +201,8 @@ def nova_import_rules(logical_line):
                 # NOTE(vish): the import error might be due
                 #             to a missing dependency
                 missing = str(exc).split()[-1]
-                if missing != mod.split('.')[-1]:
+                if (missing != mod.split('.')[-1] or
+                        "cannot import" in str(exc)):
                     _missingImport.add(missing)
                     return True
                 return False