Smoke tests occasionally fail with no obvious reason for failure.

See: https://build.gluster.org/job/smoke/30519/console

Snippet from a failing test:
12:49:00 /opt/qa/tools/posix-compliance/tests/xacl/06.t ...... ok
12:49:00 All tests successful.
12:49:00 Files=191, Tests=1960, 116 wallclock secs ( 0.72 usr  0.27 sys +  4.89 cusr  2.59 csys =  8.47 CPU)
12:49:00 Result: PASS
12:56:58 Kicking in watchdog after 600 secs
12:56:58 + finish
12:56:58 + RET=1
12:56:58 + '[' 1 -ne 0 ']'
12:56:58 + mkdir -p /d/logs/smoke
12:56:58 glusterfsd: no process killed
12:56:58 glusterd: no process killed
12:56:58 ++ date +%Y%m%d%H%M%S
12:56:58 umount: /mnt: not mounted
12:56:58 + filename=/d/logs/smoke/glusterfs-logs-20160909072658.tgz
12:56:58 + tar -czf /d/logs/smoke/glusterfs-logs-20160909072658.tgz /build/install/var/log
12:56:58 tar: Removing leading `/' from member names
12:56:58 tar: /build/install/var/log: Cannot stat: No such file or directory
12:56:58 tar: Exiting with failure status due to previous errors
12:56:58 smoke.sh returned 2
12:56:58 Build step 'Execute shell' marked build as failure
12:56:58 Finished: FAILURE


Snippet from a passing test:
12:44:10 /opt/qa/tools/posix-compliance/tests/xacl/06.t ...... ok
12:44:10 All tests successful.
12:44:10 Files=191, Tests=1960, 134 wallclock secs ( 0.95 usr  1.17 sys +  9.15 cusr 22.59 csys = 33.86 CPU)
12:44:10 Result: PASS
12:44:10 + rm -rf clients
12:44:12 + cd -
12:44:12 /home/jenkins/root/workspace/smoke
12:44:12 + finish
12:44:12 + RET=0
12:44:12 + '[' 0 -ne 0 ']'
12:44:12 + cleanup
12:44:12 + killall -15 glusterfs glusterfsd glusterd
12:44:12 + killall -9 glusterfs glusterfsd glusterd
12:44:12 glusterfsd: no process killed
12:44:12 glusterd: no process killed
12:44:12 + true
12:44:12 + umount -l /mnt
12:44:12 umount: /mnt: not mounted
12:44:12 + true
12:44:12 + rm -rf /var/lib/glusterd /etc/glusterd /build/export
12:44:12 + kill %1
12:44:12 smoke.sh returned 0
12:44:22 Process leaked file descriptors. See http://wiki.jenkins-ci.org/display/JENKINS/Spawning+processes+from+build for more information
12:44:23 Finished: SUCCESS

My best guess is that dbench is returning 1. Is this an actual possibility?