Some bugfixes

-Mainly fixes wrong names in docstrings.
-Added admin_pass parameter to the create_node() function of OpenStack_1_1_NodeDriver.
 This allows to set the root password that is assigned to a node when creating an instance with Rackspace. 
-Added some imports of with_statement to be compatible to Python 2.5.
-Fixed exception when calling list_nodes() with Brightbox.
-Added locations arguments to Brightboxs list_images() to avoid exceptions when providing a location argument.