Add 'dmctl' to default debug utilities.

dmctl can list all device mapper targets and their tables which is
extremely useful information for a bugreport. Especially to compare
the device mapper setup with the partition metadata.

Bug: 120916687
Test: 'dmctl list device -v'

Change-Id: I9e3afcf146b2814b0304f69cdf6029303beb57c7
Merged-In: I9e3afcf146b2814b0304f69cdf6029303beb57c7
Signed-off-by: Sandeep Patil <sspatil@google.com>