fix(catalyst): Take advantage of binary packages for cross toolchains.

The previous logic here only skipped the bootstrap if the toolchain
packages were already installed (which won't happen on the build host)
but we can also skip the bootstrap if binary packages are available
(which will happen on the build host). This will help avoid needless gcc
rebuilds :)
feat(build_library): Add --upload_path option to override default

This will be used to upload the latest images built from master, we
don't need every build so we just want to upload to a 'master'
directory, not one named for the current version.
Merge pull request #31 from marineam/toolchain

Script updates