Update command_executer.py to allow a silent execution mode,
where it does not attempt to write any logs.

Update auto_delete_nightly_test_data.py to use the
command_executer in silent mode (so it doesn't run out of space
writing logs on the disk it is trying to clean up).

Change-Id: Id1c2c5f171a2d3854d3b53516ead31050da647b4
Reviewed-on: https://chrome-internal-review.googlesource.com/195877
Reviewed-by: Han Shen <shenhan@google.com>
Commit-Queue: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
2 files changed