Pin test-requirements to match OpenStack requirements

A new release of flake8 is causing lint faiures. Stable branches
should have requirements pinned anyway.

This patch pins to the current stable/mitaka requirements from
the OpenStack requirements repository.

Change-Id: I494cb9bdde371e1e0a95633c8c0c78d0eb73a14b

test-requirements.txt

@@ -1,9 +1,9 @@
 ansible-lint<=2.3.9
 ansible>=1.9.1,<2.0.0,!=1.9.6
-bashate
-flake8
+bashate==0.4.0
+flake8>2.4.1,<2.6.0
 
 # this is required for the docs build jobs
-sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2
-oslosphinx>=2.5.0 # Apache-2.0
+sphinx>=1.1.2,!=1.2.0,!=1.3b1,<1.3  # BSD
+oslosphinx>=2.5.0,!=3.4.0  # Apache-2.0
 reno>=0.1.1 # Apache-2.0