Report all swarming and isolate fatal errors in a consistent way.

It makes them easier to extract with regular expressions in log parsing tools.

BUG=309661

Review URL: https://codereview.chromium.org/51383003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/swarm_client@231704 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed