Fixes LP Bug#899383 - Cleanup config file search

Cleans up a bunch of configuration-related errors
when trying to run tempest out of the box with a
simple call to:

$> nosetests storm

* Raises a sensible error if the config file cannot be found
* Makes it possible to set the config file directory and
  config file name via environment variables
* Removes unnecessary calls to create storm.config.StormConfig()
  and share a configuration object by passing the openstack.Manager's
  config object with the various rest client objects
* Updates the README to show how to make a config file and run
  the tests in tempest

Change-Id: I60e33595b88df596cc9585bcaf18d37ae77d6f2b
diff --git a/storm/tests/test_flavors.py b/storm/tests/test_flavors.py
index 590bac3..5153693 100644
--- a/storm/tests/test_flavors.py
+++ b/storm/tests/test_flavors.py
@@ -10,7 +10,7 @@
     def setUpClass(cls):
         cls.os = openstack.Manager()
         cls.client = cls.os.flavors_client
-        cls.config = storm.config.StormConfig()
+        cls.config = cls.os.config
         cls.flavor_id = cls.config.env.flavor_ref
 
     @attr(type='smoke')