tst: Provide test for ppoll

This change adds new test to assess ppoll()'s timeout related
functionality (the struct pollfd does not provide valid fd to wait
for - just wait for timeout).

To be more specific - two use cases are checked:
- if ppoll() times out immediately when passed struct timespec has zero
values of tv_nsec and tv_sec.
- if ppoll() times out after timeout specified in passed argument