bdk: add adb and fastboot commands.
Adds `bdk adb` and `bdk fastboot` which just pass the command through
to the built executables.
Argument parsing is not great due to argparse weirdness with optional
args being passed to argparse.REMAINDER, so "--" is required if the
first passthrough arg is optional, e.g.:
bdk2 root adb -- -s <serial> shell
This is a general problem and should be figured out for the bdk overall
at some point: http://b/27795688.
Bug: 27762941
Bug: 27763523
Change-Id: I1f305c6901559d7b5062f570c1db1ce93a40eba7
Test: bdk2 root adb [command]
Test: bdk2 root fastboot [command]
2 files changed
