xenserver: allow dom0 traffic in secure pool host when controller unavailable.

xenserver: allow dom0 traffic in secure pool host when controller unavailable.

A pool configured for secure fail-mode can block dom0 traffic on hosts joining
the pool or if the host reboots while the controller is unavailable.  This
commit sets default flows on a host under these conditions to allow management
traffic.  Once the connection with the controller is re-established, these
default flows are replaced by the controller.

tests/interface-reconfigure.at updated by Ben Pfaff.

NIC-376.

Signed-off-by: David Tsai <dtsai@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>