Use fixtures.TempDir
Use fixtures.TempDir

This change replaces tempfile.mkdtemp by fixtures.TempDir in order to
explicit that unittest temporary directories will be deleted (currently
the cleanup is hidden in NestedTempfile call in
openstack.tests.unit.base)

Change-Id: I76b9bbf87fa687c2a4607c75e129c9a648f29621

openstack/python-openstacksdk,briancurtin/python-openstacksdk,dtroyer/python-openstacksdk,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,openstack/python-openstacksdk,stackforge/python-openstacksdk,briancurtin/python-openstacksdk