Update release to 3.7.0
Update release to 3.7.0

Due to Openstack Release policies, the next release needs
to be a minor release, thus bumping to 3.7.0.

Change-Id: If52d48908cfd47c5b94265ebd9ab8e3289c7b19c

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