Follow the new PTI for document build

For compliance with the Project Testing Interface as
described in [1]:
[1] https://governance.openstack.org/tc/reference/project-testing-interface.html
For more detials information, please refer to [2]:
[2] http://lists.openstack.org/pipermail/openstack-dev/2017-December/125710.html

Change-Id: I648a78396a2e27f1d7197e89cddba73f8aa858aa

doc/requirements.txt

@@ -0,0 +1,6 @@
+# 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.
+openstackdocstheme>=1.17.0 # Apache-2.0
+reno>=2.5.0 # Apache-2.0
+sphinx>=1.6.2 # BSD

test-requirements.txt

@@ -2,10 +2,6 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
-# needed for doc build
-sphinx>=1.6.2 # BSD
-openstackdocstheme>=1.17.0 # Apache-2.0
-reno>=2.5.0 # Apache-2.0
 mock>=2.0.0 # BSD
 coverage!=4.4,>=4.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0

tox.ini

@@ -133,9 +133,14 @@ deps = {[tempestenv]deps}
 commands = {posargs}
 
 [testenv:docs]
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/doc/requirements.txt
 commands =
-    rm -rf doc/build
-    python setup.py build_sphinx {posargs}
+  rm -rf doc/build
+  sphinx-build -b html doc/source doc/build/html
+whitelist_externals = rm
 
 [testenv:pep8]
 commands =
@@ -161,9 +166,15 @@ enable-extensions = H106,H203,H904
 import-order-style = pep8
 
 [testenv:releasenotes]
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/doc/requirements.txt
 commands =
-    rm -rf releasenotes/build
-    sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+  rm -rf releasenotes/build
+  sphinx-build -a -E -W -d releasenotes/build/doctrees \
+         -b html releasenotes/source releasenotes/build/html
+whitelist_externals = rm
 
 [testenv:pip-check-reqs]
 # Do not install test-requirements as that will pollute the virtualenv for