Update global requirements
Update global requirements

Pin reno version to reno!=2.0.0,!=2.3.1,>=1.8.0
Pin sphinx version to sphinx!=1.6.1,>=1.5.1
reno=2.3.1 and sphinx=1.6.1 break releasenotes and doc tests.

Change-Id: I9daab4d970f387ae20ded1bf920ec3b98c7e4597

openstack/puppet-tripleo,openstack/puppet-tripleo,openstack/puppet-tripleo