lisa/tests: eas_behaviour: Make rtapp profile construction less obfuscated

This is where it would've been nice to operate on an instance of an
object, so that we could use e.g. `self.{min,max}_cap_cpus[0]`, but we
have to live with classmethods (or
`cls.get_{min,max}_cap_cpus(plat_info)[0]`, which is too wordy for me).