ovs-ctl: Add option to delete transient ports.

ovs-ctl: Add option to delete transient ports.

When using virtualization, new ports are created and removed all the time. These
ports do not persist after a system reboot, for example. They may be created
again by the virtualization manager, but that will happen after the vswitch is
already running, and the virtualization manager will add them again to the
bridge.

If a reboot happens without properly deleting such ports, all kinds of errors
will happen. The absence of the ports will be logged as errors, and adding those
ports again to the database will fail.

Deleting all bridges may not be an option, if the system cannot persist other
information outside of OVSDB.

This patch introduces the notion of transient ports. Ports may be added as
transient, as a boolean in other_config smap. When openvswitch is started by
using --delete-transient-ports ovs-ctl option, all transient ports will be
removed.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>