ovs-ctl: Add new option to use short hostname.

ovs-ctl: Add new option to use short hostname.

Current ovs-ctl forces to set full hostname in external-ids. In
some situation users may want to set short hostname. For example,
in OpenStack - OVN integration, Neutron uses the host-id provided
by Nova, which is usually short hostname, to set "requested-chassis"
in OVN. The mismatch in hypervisor's external-ids:hostname setting
causes OVN port binding failure. It can be overridden to short name
but a openvswitch restart using ovs-ctl would again set it to full
hostname. This patch ensures in such use cases --no-full-hostname
can be specified to ovs-ctl to set short hostname instead.

Signed-off-by: Han Zhou <hzhou8@ebay.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>