Don't log 'Exit code: 0'
Don't log 'Exit code: 0'

A regular gate run shows this was logged ~2500 times.
It doesn't provide any useful information since the
command executed successfully and we can see the
issued command in the debug statement before it.

Partial-Bug: #1707307
Change-Id: I431d6a59ce36deb9a5fb9deef39655d28d71f24d

mahak/neutron,huntxu/neutron,openstack/neutron,mahak/neutron,eayunstack/neutron,noironetworks/neutron,openstack/neutron,noironetworks/neutron,openstack/neutron,eayunstack/neutron,mahak/neutron,huntxu/neutron