netconf: Add dhcp support for iproute2 configurator

This patch enables iproute2 configure ip address via dhcp.

Change-Id: Iea88e8693e47fa51edb89c33344332c88c5c964d
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/15492
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>