openstack: document openstack_connection_kwargs
openstack: document openstack_connection_kwargs

OpenStackDriverMixin has a openstack_connection_kwargs() method.
Document what it does.

mistio/libcloud,Kami/libcloud,ByteInternet/libcloud,mistio/libcloud,Scalr/libcloud,Scalr/libcloud,apache/libcloud,andrewsomething/libcloud,ByteInternet/libcloud,Scalr/libcloud,StackPointCloud/libcloud,andrewsomething/libcloud,StackPointCloud/libcloud,Kami/libcloud,Kami/libcloud,apache/libcloud,andrewsomething/libcloud,mistio/libcloud,StackPointCloud/libcloud,apache/libcloud,ByteInternet/libcloud