add test for invocation via kernel param

[jamuir]

The recommended way of running systemd-bootchart is via the kernel parameter "init=/usr/lib/systemd/systemd-bootchart", as described here:

https://github.com/systemd/systemd-bootchart/blob/main/man/systemd-bootchart.xml

Running using "init=" seems to have been broken for some time on switch-root systems (at least since systemd v251).

A test should be added to exercise "init=".

[jamuir]

It might be that invocation using "init=..." is not recommended on switch-root systems.

In that case, a test could be added that uses the kernel param "rdinit=..."

[jamuir]

I see that Fedora publishes qemu images. One of those images could be used to implement kernel param tests.