Automatically detect Linux install type

[scudette]

Currently there are two flavors of Linux startup services: Sysv is for older mostly redhat systems and systemd is for more modern systems. We can build two types of RPM using the --sysv flag.

However in practice it is sometimes difficult to selectively send the right type of RPM to the right systems - it would be easier if we could just send the same RPM to all systems and have it figure out which type of startup script to use based on the system itself.

Maybe this should be done by presubmit scripts. This will make is a lot easier to deploy as we can use the same RPM to all systems in the fleet.