Replace deprecated UPPER_CONSTRAINTS_FILE variable

UPPER_CONSTRAINTS_FILE is old name and deprecated
-https://zuul-ci.org/docs/zuul-jobs/python-roles.html#rolevar-tox.tox_constraints_file
This allows to use lower-constraints file as more
readable way instead of UPPER_CONSTRAINTS_FILE=<lower-constraints file>.

Change-Id: Ia3ffea39c995978babaafc9aa5a463e5f3eda1c0

tox.ini

@@ -8,21 +8,21 @@ ignore_basepython_conflict = True
 basepython = python3
 # TODO(yasufum) Remove following definitions after tosca-parser and
 # heat-translator have its own devstack scripts.
-#   * `UPPER_CONSTRAINTS_FILE` in setenv
+#   * `TOX_CONSTRAINTS_FILE` in setenv
 #   * `-r{toxinidir}/requirements-extra.txt` in [testenv], [testenv:docs] and
 #     [testenv:lower-constraints] sections.
 setenv = VIRTUAL_ENV={envdir}
          OS_LOG_CAPTURE={env:OS_LOG_CAPTURE:true}
          OS_STDOUT_CAPTURE={env:OS_STDOUT_CAPTURE:true}
          OS_STDERR_CAPTURE={env:OS_STDERR_CAPTURE:true}
-         UPPER_CONSTRAINTS_FILE={toxinidir}/upper-constraints.txt
-passenv = UPPER_CONSTRAINTS_FILE
+         TOX_CONSTRAINTS_FILE={toxinidir}/upper-constraints.txt
+passenv = TOX_CONSTRAINTS_FILE
 usedevelop = True
 whitelist_externals = rm
 install_command =
     pip install -U {opts} {packages}
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/requirements-extra.txt
   -r{toxinidir}/test-requirements.txt
@@ -103,7 +103,7 @@ commands =
 [testenv:cover]
 setenv =
     PYTHON=coverage run --source tacker --parallel-mode
-    UPPER_CONSTRAINTS_FILE={toxinidir}/upper-constraints.txt
+    TOX_CONSTRAINTS_FILE={toxinidir}/upper-constraints.txt
 commands =
     stestr run {posargs}
     coverage combine