Fix tox.ini to correctly test lower-constraints

Due to the way we currently define install_command, all test targets
are using upper-constraints, including the lower-constraints one.
This patch fixes it and adds standard things like passing proxy settings.

Change-Id: I61c3b45ae591ea44688f29598cb8b802bb094423
(cherry picked from commit 91ed55678e)

tox.ini

@@ -5,15 +5,19 @@ envlist = py3,py27,functional,pep8
 
 [testenv]
 usedevelop = True
-install_command = pip install -U -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/stable/rocky/upper-constraints.txt} {opts} {packages}
+install_command = pip install -U {opts} {packages}
 setenv =
   VIRTUAL_ENV={envdir}
   PYTHONDONTWRITEBYTECODE = 1
   OS_TEST_PATH=./ironic_python_agent/tests/unit
   LANGUAGE=en_US
   LC_ALL=en_US.utf-8
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/rocky}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/test-requirements.txt
 commands = stestr run {posargs}
+passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:functional]
 basepython = python3