Add passenv to tox.ini to make functests run with tempauth

Since tox version 2.0.0 env vars are not passed to the test
env, which means that the SWIFT_TEST_CONFIG_FILE var is not
passed in to tox -e func env. That means that both times
tox -e func runs it is using keystone auth, and never using
tempauth.

Related-Bug: 1455102

Co-Authored-By: Christian Schwede <cschwede@redhat.com>

Change-Id: I23dcdbcde0bf8adc9429eb2d294a2c778005d136

tox.ini

@@ -11,6 +11,7 @@ setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py testr --testr-args="{posargs}"
+passenv = SWIFT_* *_proxy
 
 [testenv:pep8]
 commands =