Previously, RPMS built on Amazon Linux would point to the improper ruby directory, or would have improper dependencies.
Use %{amzn} as a rpm macro to determine if the
rpm is being built on an Amazon Linux distro.
If %{amzn} is set, use the Fedora/RHEL7 method
of discovering ruby lib directory. Use the
RHEL 6 init system (sysvinit). Use the RHEL 5
libselinux-ruby dependency.