LU-2550 test: fix sanity test_122

The injected error in sanity test_122 could cause reconnect & resend
infinitely, then the test will wait on 'sync' forever.

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes testlist=sanity

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: I53f0a476c98904e9fb570cf9e13ccdacdcd80af0
Reviewed-on: http://review.whamcloud.com/5050
Tested-by: Hudson
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>