dmctl: Add verbose 'dmctl list devices'

This adds an option to list device mapper devices including their
current target table. Useful to be included in bugreport to
map the logical partitions metadata with actual device mapper setup.

Bug: 120916687
Test: dmctl list devices -v

Change-Id: I091666506d24372d1e111ffa1c0256c8bbff0c5e
Signed-off-by: Sandeep Patil <sspatil@google.com>