tests: (helpers) simple tool to create a child process

tests: (helpers) simple tool to create a child process

This basic helper program can be used to create a child process
to test process attribute inheritances between parent and
child processes, e.g. real-time scheduling attributes with chrt(1)
or utilization clamp settings with uclampset(1), where options
like --reset-on-fork need to be tested.

Signed-off-by: Christian Goeschel Ndjomouo <cgoesc2@wgu.edu>