curl to tar to avoid the file having a location

At least in travis it wasn't landing where expected so when trying to
expand the archive a failure would occur.

tox.ini

@@ -68,8 +68,7 @@ basepython = python2.7
 deps = tox
 commands = -mkdir {envdir}/src
            -rm -r {envdir}/src/*
-           curl -o {envdir}/src/nova.tar.gz https://tarballs.openstack.org/nova/nova-master.tar.gz
-           tar -C {envdir}/src -zxv --strip-components 1 -f nova.tar.gz
+           bash -c "curl https://tarballs.openstack.org/nova/nova-master.tar.gz | tar -C {envdir}/src -zxv --strip-components 1 -f - "
            tox -c {envdir}/src -e functional --notest  # ensure a virtualenv is built
            {envdir}/src/.tox/functional/bin/pip install -U {toxinidir}  # install gabbi
            tox -c {envdir}/src -e functional test_placement_api
@@ -77,6 +76,8 @@ whitelist_externals =
     mkdir
     curl
     tar
+    rm
+    bash
 
 [testenv:docs]
 commands =