Updated openstack/openstack

Project: openstack/nova-specs  f49397be06404d310483f49b2c062c8b3dd70767

Uncap sphinx version

Sphinx version has been capped since
I9c45d239e156ec4fb49b5d8bd2404b66155be92b
in order to fix an issue with resolving citations.

Then, in I7e55dcf910e0ba6dd85b565db8cb1ecbdd39634a,
the issue has been fixed by modifying citation references.

So uncap sphinx version.
But sphinx 1.6.1 has another issue (*1),
so leave sphinx 1.6.1 in the blacklist.

*1: sphinx-doc/sphinx#3754

Change-Id: I09acc562bc37edc3c8a40027f7eb359aaa956c32
Related-Bug: #1695127