kill dnsmasq to avoid conflict with dhcpd

libvirt start dnsmasq to provide dhcp service on virbr0,
but unfortunately it by default binds on all interfaces.
to avoid conflict with dhcpd started by cobbler later, kill all
dnsmasq since it won't be used by ci anyway.

Change-Id: I006f6c3e3493a34c4770cff0b35ee8f4b2b5293c
Merge "kill dnsmasq to avoid conflict with dhcpd" into dev/experimental