labs: use sudo for "killall dnsmasq"
labs: use sudo for "killall dnsmasq"

Killing the dnsmasq process requires root privileges.

Change-Id: I161823337b225cb8e39b2bd51d5472f65bbb3a16

openstack/training-labs,openstack/training-labs,dguitarbite/OpenStack-Labs,openstack/training-labs,dguitarbite/OpenStack-Labs,dguitarbite/OpenStack-Labs