ovn-controller-vtep.at: Fix intermittent test failure.

When testing the recreation of 'chassis' table entry by 'ovn-controller-
vtep'.  The removal of 'chassis' table entry by the 'ovn-sbctl' could
cause 'Broken pipe' warning in ovsdb-server.log.  This is due to the
race between 'ovn-sbctl' exiting and 'ovn-controller-vtep' adding
the chassis back.  So, if the 'ovn-sbctl' exits right when the
ovsdb-server tries to send update of readd of the deleted 'chassis',
the sending will fail with 'Broken pipe' error.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Russell Bryant <rbryant@redhat.com>

tests/ovn-controller-vtep.at

@@ -104,6 +104,10 @@ OVS_WAIT_UNTIL([test -n "`grep WARN ovn-controller-vtep.log`"])
 AT_CHECK([sed -n 's/^.*\(|WARN|.*\)$/\1/p' ovn-controller-vtep.log], [0], [dnl
 |WARN|Chassis for VTEP physical switch (br-vtep) disappears, maybe deleted by ovn-sbctl, adding it back
 ])
+# this removal of chassis could cause 'Broken pipe' warning in the ovsdb-server.log,
+# due to the race between 'ovn-sbctl' exiting and 'ovn-controller-vtep' adding
+# the chassis back.  so just removes the 'Broken pipe' warning from ovsdb-server.log.
+AT_CHECK([sed -i '/Broken pipe/d' ovsdb-server.log])
 
 # changes the tunnel_ip on physical switch, watches the update of chassis's
 # encap.