Bump python-openstackclient to 3.1.0
Bump python-openstackclient to 3.1.0

OSC 3.1.0 released and bumped in upstream: https://review.openstack.org/361070
Change-Id: Iffceed5cff3591de47350e852dbd08204d6ec4a5

redhat-openstack/rdoinfo,javierpena/rdoinfo