Log output of lsblk cmd if test_device_tagging failed

test_device_tagging has been failing twice in the last 48h with
the following error: "mount: mounting /dev/sr0 on /mnt failed: Device or
resource busy".

Add the result of the lsblk command to see whether /dev/sr0 exists
and /mnt is not already mounted.

Change-Id: I7067b87cad79f98cdf6eff83809d96dd0ac3ed2f
1 file changed