Revert "Update setuptools to 36.2.0"

Our pip, setuptools, wheel install process is seperate
from the installation of other packages, so it still
works. The problem comes in when you try to up/downgrade
setuptools at the same time as installing other packages.
This problem was prevalent when doing docs/linters tests.

This reverts commit d4ae08646d
and removes the constraint from the tox config so that doc
and linter tests will not try to force a up/downgrade for
these packages.

Change-Id: I27f843d443b32c52b5f9ec6be581a9366c8dbcf5

global-requirement-pins.txt

@@ -10,5 +10,5 @@
 ### These pins are updated through the sources-branch-updater script ###
 ###
 pip==9.0.1
-setuptools==36.2.0
+setuptools==33.1.1
 wheel==0.29.0

tox.ini

@@ -8,7 +8,7 @@ envlist = linters,docs,releasenotes,inventory,py3-inventory
 usedevelop = True
 basepython = python2.7
 install_command =
-    pip install -c{toxinidir}/global-requirement-pins.txt -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
+    pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 deps =
     -r{toxinidir}/global-requirement-pins.txt
     -r{toxinidir}/test-requirements.txt