Added get_memory_percent() test cases. Also added coverage for other functions (get_cpu_percent(), get_cpu_times()  is_running()), in zombie_process and fetch_all tests.
Added get_memory_percent() test cases.
Also added coverage for other functions (get_cpu_percent(), get_cpu_times()  is_running()), in zombie_process and fetch_all tests.

ztop/psutil,ztop/psutil,ztop/psutil,ztop/psutil