tests: make ovn logical router test case more reliable

tests: make ovn logical router test case more reliable

The "ovn -- 1 HVs, 2 LSs, 1 lport/LS, 1 LR" test case creates a
configuration including a logical router, then:
    1) Sends a packet that is expected to be forwarded by the
       logical router.
    2) Disables the logical router.
    3) Sends another packet, identical to the one sent in (1), that
       should not be forwarded.

This test case fails intermittently, apparently because the disabling
of the logical router in (2) has not yet been propagated to the
forwarding plane at the time the second packet is sent. (When the
failure occurs, two packets are captured whereas only one is expected.)

Address this issue by adding a one second sleep between steps (2) and
(3). Adding a sleep does not actually fix anything, but it
does make this test case more likely to work correctly.

In one series of tests, this test case failed 11 times out of 20
without this fix and succeeded 20 times out of 20 attempts with
this fix.

Fixes: 5412db307420 ("ovn: Add column enabled to table Logical_Router")
Signed-off-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: Russell Bryant <russell@ovn.org>