test-ovsdb: Log steps in idl test.

test-ovsdb: Log steps in idl test.

Until now, "test-ovsdb idl" has printed the steps that it goes through
to stdout.  This commit also makes it log the same information.  This
makes it easier to match up the steps with the rest of the log (in
particular with the jsonrpc logging).

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Ilya Maximets <i.maximets@ovn.org>