Adding the logic to use the isolated output directory.
This change introduces the following behavior:
- The ISOLATED_OUTDIR is passed to each binary as --output-dir
- All subprocess' stdout and stderr are logged to the output dir
- All files in output dir are automatically uploaded to the controller after
testing completes
- Unit tests for the new functionality
- Supplementary RPC methods added
BUG=510092
Review URL: https://codereview.chromium.org/
1229843003
Cr-Commit-Position: refs/heads/master@{#338876}