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/services/nova/json/images_client.py b/storm/services/nova/json/images_client.py
index e8a1326..59e9269 100644
--- a/storm/services/nova/json/images_client.py
+++ b/storm/services/nova/json/images_client.py
@@ -6,10 +6,10 @@
 
 class ImagesClient(object):
 
-    def __init__(self, username, key, auth_url, tenant_name=None):
-        self.client = rest_client.RestClient(username, key,
+    def __init__(self, config, username, key, auth_url, tenant_name=None):
+        self.config = config
+        self.client = rest_client.RestClient(config, username, key,
                                              auth_url, tenant_name)
-        self.config = storm.config.StormConfig()
         self.build_interval = self.config.nova.build_interval
         self.build_timeout = self.config.nova.build_timeout
         self.headers = {'Content-Type': 'application/json',