ovn: Support chassis hostname in requested-chassis.

ovn: Support chassis hostname in requested-chassis.

Previously, OVN expected the Chassis "name" in the "requested-chassis"
option for a Logical_Switch_Port.  It turns out that in the two OVN
integrations I've checked with that plan to use this option,
specifying the Chassis "hostname" is much more convenient.  This patch
extends the "requested-chassis" option to support both the Chassis
name or the hostname as a value.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Lance Richardson <lrichard@redhat.com>