Fix coglet runtime boot failures
- Fix binary path in go_cog.py to use cog/bin/coglet-server-{os}-{arch}
- Add 'pip uninstall cog' before coglet install to avoid conflicts with
pre-installed cog in base images (e.g. r8.im/cog-base)
- Add wheel count assertion to prevent stale wheels from being embedded
- Clean old wheels in build-wheels script before building new ones
