[bugfix]tc006 failed due to volume attached to different location "/dev/vdc"

[bugfix]tc006 failed due to volume attached to different location "/dev/vdc"

JIRA: YARDSTICK-857

The yardstick test suites are failing for os-odl-bgpvpn-ha and os-odl-bgpvpn-noha scenarios installed with apex.
Here are the yardstick test run logs:
os-odl-bgpvpn-ha: https://build.opnfv.org/ci/job/yardstick-apex-baremetal-daily-master/624//consoleFull, https://build.opnfv.org/ci/job/yardstick-apex-baremetal-daily-master/640//consoleFull
os-odl-bgpvpn-noha: https://build.opnfv.org/ci/job/yardstick-apex-baremetal-daily-master/637//console

The root cause of the problem is in some environment the block device cannot be attached to the target path.
In this patch, the actually device path is found and used.

Change-Id: I46c601960a0668c81f9b73504ef9553f9e8591dc
Signed-off-by: JingLu5 <lvjing5@huawei.com>