make test: Adding FAKEIPMI

Since commit 2551b165206701abdad46c304071776fde42485f, the FAKEIPMI
argument is required to play with fake-ipmi devices.

This does make the test target working again.
try_match: Adding an inline documentation

When trying to debug a spec and an hw file it's always much boring
trying to remember what are the arguments orders while not reading the
code.

Instead of getting an exception, let's print a useful help message if
not the good amount of arguments are passed.