Allow non-default controller-dhcp-enabled at init

Allow non-default controller-dhcp-enabled at init

Currently controller-dhcp-enabled cn only be set through yang and defaults
to false. To change one must wait for bundles to come up and change
through restconf. This adds option to specif a different default at bring
up.

To set the default for controller-dhcp-enabled:

1. Change the value in dhcpservice/.../netvirt-dhcpservice.xml
2. Copy the file into the unzipped distribution before starting karaf:
  cd netvirt/vpnservice
  mkdir -p ./distribution/karaf/target/assembly/etc/opendaylight/datastore/initial/config
  cp dhcpservice/impl/src/main/resources/netvirt-dhcpservice.xml ./distribution/karaf/target/assembly/etc/opendaylight/datastore/initial/config

Change-Id: I6768e117515a4ff2c52e70961efb3aeac65c8d5f
Signed-off-by: Vishal Thapar <vishal.thapar@ericsson.com>
(cherry picked from commit d115bc161fe0d562c23ae5d041778590616ca88d)