Whitelist commands in tox.ini

Fix these warnings when invoking "tox -e jjb":
WARNING:test command found but not installed in testenv
  cmd: /usr/bin/rm
  env:
/home/aj/Software/vcs/OpenStack/openstack-infra/project-config/.tox/jjb
Maybe forgot to specify a dependency?
jjb runtests: commands[1] | mkdir -p
/home/aj/Software/vcs/OpenStack/openstack-infra/project-config/.tox/jjb/tmp
WARNING:test command found but not installed in testenv
  cmd: /usr/bin/mkdir
  env:
/home/aj/Software/vcs/OpenStack/openstack-infra/project-config/.tox/jjb
Maybe forgot to specify a dependency?

Change-Id: If1b56882d3b608450d2ab5fbf0af5cbe920471e8
Merge "Whitelist commands in tox.ini"