Some cleanup to slave_utils.py.
Some cleanup to slave_utils.py.

- Add linux3 to platform detection (for linux 3.x kernels).
- Replace sconsbuild with out.
- Remove code that strips symbols from TestShell.app-- this is done
  during the build and we don't even run TestShell.app anymore.

Review URL: http://codereview.chromium.org/8505023

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@109276 0039d316-1c4b-4281-b951-d872f2087c98

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