Remove useless str()
Remove useless str()

This change uses:

  LOG.exception(_LE("... %s"), cmd)

instead of:

  LOG.exception(_LE("... %s"), str(cmd))

because %s converts python object using str.

Change-Id: I19c21f6e357f3cba3f5937f63a690628205d5e5b

noironetworks/neutron,mahak/neutron,mahak/neutron,openstack/neutron,sebrandon1/neutron,mahak/neutron,openstack/neutron,igor-toga/local-snat,cloudbase/neutron,huntxu/neutron,huntxu/neutron,sebrandon1/neutron,igor-toga/local-snat,openstack/neutron,eayunstack/neutron,cloudbase/neutron,noironetworks/neutron,eayunstack/neutron