ovn-northd: Don't set custom log level defaults.

ovn-northd: Don't set custom log level defaults.

ovn-northd set some custom log level defaults, which I believe were
copied from ovs-vsctl.  Other daemons don't set this.  The difference in
behavior in ovn-northd vs other daemons has caused some confusion during
OpenStack+OVN development and testing, so make it consistent.

Reported-by: Ryan Moats <rmoats@us.ibm.com>
Reported-at: https://bugs.launchpad.net/bugs/1539994
Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-By: Kyle Mestery <mestery@mestery.com>
Acked-by: Ben Pfaff <blp@ovn.org>