tox needs to pull from stable/queens

Updates the tox.ini to pull from nova's stable/queens branch
instead of master. This should have been done when we first
branched queens here, but was missed.

Change-Id: Ifdc23f94a8448e12252ce73a436fcf4049d4f7b3

tox.ini

@@ -12,8 +12,8 @@ deps =
        -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/queens}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-       -egit+https://github.com/openstack/nova#egg=nova
-       -rhttps://raw.githubusercontent.com/openstack/nova/master/test-requirements.txt
+       -egit+https://github.com/openstack/nova@stable/queens#egg=nova
+       -rhttps://raw.githubusercontent.com/openstack/nova/stable/queens/test-requirements.txt
 whitelist_externals = bash
 commands = bash tools/pretty_tox.sh '{posargs}'