modify test-requirement according to requirements project

the OpenStack requirements project has modify version requirement of docutils/oslosphinx.
The link is below
https://review.openstack.org/#/c/418772/
So modify test-requirement like other project
Closes-Bug: #1666149

Change-Id: Ie9acf0408f8081b5275bb272a1864c4880280869

test-requirements.txt

@@ -2,8 +2,8 @@ coverage>=3.6
 pep8==1.5.7
 pyflakes==0.8.1
 flake8==2.2.4
-docutils>=0.11,!=0.13.1  # OSI-Approved Open Source, Public Domain
-sphinx>=1.1.2,!=1.2.0,<1.3
+docutils>=0.11  # OSI-Approved Open Source, Public Domain
+sphinx>=1.5.1
 httmock>=1.2.4
 mock
 oslotest>=1.2.0 # Apache-2.0