Switch from oslosphinx to openstackdocstheme

As part of the docs migration work[0] for Pike we need to switch to use
the openstackdocstheme.

[0]https://review.openstack.org/#/c/472275/

Change-Id: I18e7db0410ffa28d6a62a1adfb1a7eabe610c950
diff --git a/test-requirements.txt b/test-requirements.txt
index 7c97fa7..0639513 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -4,7 +4,7 @@
 hacking>=0.12.0,!=0.13.0,<0.14  # Apache-2.0
 
 sphinx>=1.2.1,!=1.3b1,<1.4  # BSD
-oslosphinx>=4.7.0 # Apache-2.0
+openstackdocstheme>=1.11.0 # Apache-2.0
 reno>=1.8.0 # Apache-2.0
 mock>=2.0 # BSD
 coverage>=4.0 # Apache-2.0