Add --logging_level option to crosperf.

Add --logging_level={verbose, average, quiet} option to crosperf,
optionally reducing the amount of logging output.  "verbose" gives
the same output Crosperf always gave; "quiet" gives minimal output, and
"average" is in the middle. The default for now is "verbose". Doing this
also involved adding logging levels to the command_executer, and to
image_chromeos (again, with the default being "verbose").

BUG=None
TEST=Tested all three levels of logging, with and without having to
reimage the DUT.  It all worked properly.

Change-Id: Icf8c9a6831fe25202adcb624c6c7e1d1a7ac25a5
Reviewed-on: https://chrome-internal-review.googlesource.com/156883
Reviewed-by: Caroline Tice <cmtice@google.com>
Commit-Queue: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
15 files changed