Add --json option to generate normalized JSON with slaves information.
Add --json option to generate normalized JSON with slaves information.

R=stip@chromium.org,iannucci@chromium.org
BUG=

Review URL: https://codereview.chromium.org/417933002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@285333 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build