Use unused client vm for new waterfall.
Use unused client vm for new waterfall.

Freeing up a slave for use in https://chromereviews.googleplex.com/8137016/

TBR=iannucci@chromium.org
BUG=270916

Review URL: https://chromiumcodereview.appspot.com/23039005

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@217668 0039d316-1c4b-4281-b951-d872f2087c98

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