Use TOX_CONSTRAINTS_FILE

UPPER_CONSTRAINTS_FILE is old name and deprecated
This allows to use upper-constraints file as more
readable way instead of UPPER_CONSTRAINTS_FILE=<lower-constraints file>.

Change-Id: I0c8c2c4a783c4f0ac9f7530d4d18937ce5b17c61

tox.ini

@@ -12,7 +12,7 @@ setenv =
    OS_STDOUT_CAPTURE={env:OS_STDOUT_CAPTURE:true}
    OS_STDERR_CAPTURE={env:OS_STDERR_CAPTURE:true}
    PYTHONWARNINGS=default::DeprecationWarning
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
@@ -20,7 +20,7 @@ commands =
            python {toxinidir}/tools/django-manage.py test bgpvpn_dashboard
 
 [testenv:releasenotes]
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
@@ -71,7 +71,7 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html