Move doc related modules to doc/requirements.txt

Change-Id: I3d2e5e2322ac8374881f76217e35792efeea073a

doc/requirements.txt

@@ -0,0 +1,8 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+
+sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD
+reno>=2.5.0
+openstackdocstheme>=1.18.1

test-requirements.txt

@@ -5,9 +5,3 @@
 hacking<0.11,>=0.10.0
 oslotest>=1.5.1
 stestr>=2.0.0
-
-# These are needed for docs generation
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD
-reno>=2.5.0
-openstackdocstheme>=1.18.1

tox.ini

@@ -39,7 +39,14 @@ commands =
 
 [testenv:docs]
 basepython = python3
-commands = sphinx-build -W -b html doc/source doc/build/html
+whitelist_externals =
+  rm
+deps =
+  {[testenv]deps}
+  -r{toxinidir}/doc/requirements.txt
+commands =
+  rm -rf doc/build
+  sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
 basepython = python3