This patch establishes the following convention:
- scripts `checkout_build_archive_upload.sh` and `upload.sh` now accept
build flavor instead of browser name. Build flavor fully defines the
build produced / uploaded.
- scripts under `//browser_patches/webkit` and
`//browser_patches/firefox` produce build that is specific to the host
system.
Both `checkout_build_archive_upload.sh` and `upload.sh` scripts now
accept a `firefox-win64` browser instead of an optional `--win64` flag.
This is a preparation before introducing `webkit-wpe` parameter in these
scripts.
