fix tox dep install
fix tox dep install

- pip no longer supports the --allow-unverified flag.
  This chnage removes it from the tox.ini file.

Change-Id: I9d746dba8d9d0711e2ffe5e464a4d1bcbdf6abe7

stackforge/networking-ovs-dpdk,openstack/networking-ovs-dpdk,openstack/networking-ovs-dpdk,stackforge/networking-ovs-dpdk,stackforge/networking-ovs-dpdk