ovn: Add ovn-ctl to assist with OVN daemon lifecycle.

ovn: Add ovn-ctl to assist with OVN daemon lifecycle.

This patch introduces ovn-ctl, which is similar to ovs-ctl.  I opted
for a new script as everything in OVN so far is nicely isolated, so a
new script seemed to make the most sense.

If you'd like to run ovn-controller on a host already running ovs:

    # ovn-ctl start_controller

If you'd like to run ovn-northd:

    # ovn-ctl start_northd

Note that ovn-ctl assumes that ovn-northd is running on the same
server as ovsdb-server hosting the OVN databases.  Based on the
current architecture this seems like a completely reasonable
assumption.  This can be improved later when needed.

There's some additional stuff happening in start_northd to make the
experience nicer and not require additional steps by the
administrator.  It creates the OVN dbs if they don't exist.  If
ovsdb-server hasn't loaded them, it tells it to load them, as well.

ovn-ctl also supports running everything on the same host.  This would
be common in a test environment with a single host or small set of
hosts.  That would simply be:

    # ovs-ctl start --system-id=random
    # ovn-ctl start_northd
    # ovn-ctl start_controller

Signed-off-by: Russell Bryant <rbryant@redhat.com>
CC: Flavio Leitner <fbl@redhat.com>
CC: Ben Pfaff <blp@nicira.com>
[blp@nicira.com added configure.ac code to create ovn/utilities builddir]
Signed-off-by: Ben Pfaff <blp@nicira.com>