don't mock `os.getpid()` and `os.getppid()` (#180)
don't mock `os.getpid()` and `os.getppid()` (#180)

This avoids masking missing implementations, e.g. `os.getppid()` on Windows
and Python 2.7

closes #180

beniwohli/apm-agent-python,beniwohli/apm-agent-python,beniwohli/apm-agent-python,beniwohli/apm-agent-python