Allow import redirections

When we move modules out of namespace packages we set up redirects to
import the new module under the old name. Python's import machinery
doesn't detect those things as modules, and the names don't show up in
sys.modules. However, if we look at what we actually got when we did the
import we can see that it is a module.

Change-Id: I4b42d081965b6d898b178cbe9232b47cfed17d8a

hacking/checks/imports.py

@@ -11,6 +11,7 @@
 #  under the License.
 
 import imp
+import inspect
 import os
 import re
 import sys
@@ -100,7 +101,20 @@ def hacking_import_rules(logical_line, physical_line, filename, noqa):
             else:
                 # NOTE(imelnikov): we imported the thing; if it was module,
                 # it must be there:
-                return mod in sys.modules
+                if mod in sys.modules:
+                    return True
+                else:
+                    # NOTE(dhellmann): If the thing isn't there under
+                    # its own name, look to see if it is a module
+                    # redirection import in one of the oslo libraries
+                    # where we are moving things out of the namespace
+                    # package.
+                    pack_name, _sep, mod_name = mod.rpartition('.')
+                    if pack_name in sys.modules:
+                        the_mod = getattr(sys.modules[pack_name], mod_name,
+                                          None)
+                        return inspect.ismodule(the_mod)
+                    return False
         return True
 
     def is_module(mod):