Don't use python with run_process
Don't use python with run_process

First noted in change id by fumihiko and kyle:
I079e18b58b214bf8362945c253d6d894ca8b1a6b

Neutron and few others seem to use an extra "python" along
with run_process which is quite unnecessary and complicates
adding python3 support in devstack. So let's clean this up.

Change-Id: I2d478f2b04c04d05c18420563e2ad77eba73be3f
group-policy/devstack,costingalan/devstack,vsham20/devstack,bigswitch/devstack,richliu/devstack,dirkmueller/devstack,richliu/devstack,pombredanne/devstack,samgoon/devstack,ozamiatin/devstack,dirkmueller/devstack,avvocatodemarchis/devstack,mssumanth/devstack,dtroyer/devstack,Mahito/devstack,openstack-dev/devstack,varunarya10/devstack,costingalan/devstack,mssumanth/devstack,thomasem/devstack,TwinkleChawla/devstack,parul24/devstack,ozamiatin/devstack,varunarya10/devstack,bswartz/devstack,dtroyer/devstack,nawawi/openstack,group-policy/devstack,Mahito/devstack,bswartz/devstack,openstack-dev/devstack,pombredanne/devstack,avvocatodemarchis/devstack,TwinkleChawla/devstack,nawawi/openstack,noironetworks/devstack,prithivm/branch01,noironetworks/devstack,bigswitch/devstack,olivierlemasle/devstack,thomasem/devstack,parul24/devstack,prithivm/branch01,olivierlemasle/devstack,vsham20/devstack,samgoon/devstack