Fix unbound local variable 'password error.

Fixes an issue causing the the following error when running tempest:

UnboundLocalError: local variable 'password' referenced before
assignment

Also, removes unused api_key param.

Change-Id: If9937a2ea51116f989316e32bb1209f9a8704a6e
diff --git a/tempest/openstack.py b/tempest/openstack.py
index 69b4e3c..d52647b 100644
--- a/tempest/openstack.py
+++ b/tempest/openstack.py
@@ -15,7 +15,7 @@
 
 class Manager(object):
 
-    def __init__(self, username=None, api_key=None, tenant_name=None):
+    def __init__(self, username=None, password=None, tenant_name=None):
         """
         Top level manager for all Openstack APIs
         """