Add max_backoff and starting_backoff for get_conn in swift service
Add max_backoff and starting_backoff for get_conn in swift service

Change-Id: I45f5d3009e0e2015c7366384ee826113fc27c70b

sohonetlabs/python-swiftclient,openstack/python-swiftclient,sohonetlabs/python-swiftclient,openstack/python-swiftclient