Today we report thread pool info using a common object. This means that
we use a shared set of terminology that is not consistent with the
terminology used to the configure thread pools. This holds in particular
for the minimum and maximum number of threads in the thread pool where
we use the following terminology:
thread pool info | fixed | scaling
min core size
max max size
A previous change addressed this for the nodes info API. This commit
changes the display of thread pool info in the cat thread pool API too
to be dependent on the type of the thread pool so that we can align the
terminology in the output of thread pool info with the terminology used
to configure a thread pool.