Use _set_instance_obj_error_state in compute manager set_admin_password

The set_admin_password operation is not a lifecycle operation like
building or deleting an instance, or resize for that matter, so replace
usage of _set_instance_error_state which does a host stats update with
_set_instance_obj_error_state which just sets the instance state to
error and handles any InstanceNotFound exception (in case we still want
to be a little paranoid).

Part of blueprint compute-manager-objects-juno

Change-Id: Ie1d1075095ed5d318d0d7a638526bc5cd40d4583
Use ebtables to isolate dhcp traffic

Iptables doesn't properly block the broadcast traffic crossing
the bridge, so use ebtables instead. Removes test which is no
longer valid since we are not using iptables anymore.

Change-Id: I43e5f1fe9512dd3ec9595c7203bc46837cef3cad
Closes-Bug: #1318104
Merge "Use _set_instance_obj_error_state in compute manager set_admin_password"
Merge "Use ebtables to isolate dhcp traffic"