Add check for mythtv-setup in mythshutdown

[Matthew Wire <devel@…>]

Adds a check for mythtv-setup in mythshutdown --status. This means mythshutdown --check will return 1 when the backend is running and the backend won't trigger an idle shutdown when I'm running mythtv-setup.

Since the maximum return value is 255 I have set it to always return 255 if setup is running. This means that if all the other checks return true it would incorrectly return true. This is very unlikely unless you are already in a wakeup period and about to enter another one while at the same time doing all the other tasks.
In other words we have run out of return values.

[paulh]

(In [14734]) Add a check for mythtv-setup running in mythshutdown --status.

Patch from Matthew Wire. Closes #4100.