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_image_metadata.py b/storm/tests/test_image_metadata.py
index 263a771..c8dff27 100644
--- a/storm/tests/test_image_metadata.py
+++ b/storm/tests/test_image_metadata.py
@@ -12,7 +12,7 @@
         cls.os = openstack.Manager()
         cls.servers_client = cls.os.servers_client
         cls.client = cls.os.images_client
-        cls.config = storm.config.StormConfig()
+        cls.config = cls.os.config
         cls.image_ref = cls.config.env.image_ref
         cls.flavor_ref = cls.config.env.flavor_ref
         cls.ssh_timeout = cls.config.nova.ssh_timeout