Improve packages to add symlinks and testing

[ober]

Currently our packages install to /opt/gerbil. As /opt/gerbil/bin is not in the default PATH, we need to add symlinks to /usr/bin for /opt/gerbil/bin binaries. Additionally we need to validate that the packages install cleanly on the distro they are intended for, and that tests pass. This is to catch any requirements the runtime may have as dependent packages.