autoupdate_EndToEnd: Improve dumping of Omaha-devserver output.

* No need to dump the stdout of the cat operation to the log, we log the
  result anyway afterwards.

* Add start/end snip markers around the text for clarity.

BUG=b:24158510
TEST=Devserver stdout and log dumped correctly in moblab run

Change-Id: I3db362ce1fd4b7183b8d70f188e66bc24b58d950
Reviewed-on: https://chromium-review.googlesource.com/304327
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
1 file changed