When running chromeos-install, after failures it's possible that
the script will automatically run various diagnostic commands
regarding the state of storage devices.  The principle purpose of
these diagnostics is to make sure that important information gets
into recovery logs.  However, If chromeos-install is invoked by a
human installing from USB, the logs tend to obscure the real error
message, without adding value.

We should change chromeos-install so that the diagnostics are only
invoked after failures during recovery, and not routinely when invoked
from a command line.  That can be accomplished with the following
changes:
 1) Make the diagnostic commands in cleanup_on_failure conditional
    upon the presence of a command line option selecting them.  By
    default, the option should omit the commands.
 2) Change chromeos-recovery to include the option on the command
    line.