Add support for swarming_client in runisolatedtest.py.
Add support for swarming_client in runisolatedtest.py.

It first looks at swarming_client, then falls back to swarm_client.

TBR=ilevy@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/20730002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@213902 0039d316-1c4b-4281-b951-d872f2087c98

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