Add configured list of offline slaves.
Add configured list of offline slaves.

TBR=cmp@chromium.org, nsylvain@chromium.org
BUG=None
TEST=local start

Review URL: https://chromiumcodereview.appspot.com/10875068

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@153388 0039d316-1c4b-4281-b951-d872f2087c98

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