net_config: use vdscli and setupNetworks

This patch replaces the usage of the vdsm command line interface
with the python vdsm.vdscli and, in the process, switches from
the non-rolling-back (and deprecated) addNetwork API verb to
th rolling-back setupNetworks.

Change-Id: Ic1923870adcb81f4e6bb5c6c1cc819d2e6e49aa2
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>