dump CI failures with kpartx and no /dev/loop devices

dump CI failures with kpartx and no /dev/loop devices

CI is failing due to unable to find loop device for kpartx

"cmd": [
    "kpartx",
    "-l",
    "/tmp/workspace/yardstick/yardstick-xenial-server.raw"
]

"stderr": "mount: could not find any device /dev/loop#Bad address\ncan't set up loop",

This error occurs when kpartx can't find any loop devices to use

https://build.opnfv.org/ci/job/yardstick-compass-virtual-daily-master/3261/console

JIRA: YARDSTICK-1054
JIRA: YARDSTICK-1096

Change-Id: Ib6131ce29c4f9e81386eb5471dd6107825798620
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>