Move sphinx + deps to doc/requirements.txt

Move all doc related requirements to a separate requirements.txt so
that the tests do not install unneccessary dependencies.

Change-Id: I276775ee2d038209f82bfb42dca386a2f5bf02f0

doc/requirements.txt

@@ -0,0 +1,4 @@
+sphinx>=1.5.1,<1.6
+sphinxcontrib-programoutput
+sphinxcontrib-httpdomain
+reno>=2.5.0 # Apache-2.0

test-requirements.txt

@@ -1,10 +1,6 @@
 # Nodepool uses hacking for its dependencies
 hacking>=0.10.2,<0.11
 coverage
-sphinx>=1.5.1,<1.6
-sphinxcontrib-programoutput
-sphinxcontrib-httpdomain
-reno>=2.5.0 # Apache-2.0
 fixtures>=0.3.12
 mock>=1.0
 python-subunit

tox.ini

@@ -45,6 +45,8 @@ commands =
 
 [testenv:docs]
 basepython = python3
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-build -W -d doc/build/doctrees -b html doc/source/ doc/build/html