Renamed 'check_all_disks' to 'check_all_disks_param', added sysstat support

While integrating with Icinga I got an error that the command 'check_all_disks_param' was unknown. I found a discrepancy between how it's used in NRPE and Icinga. Because it's used multiple times in Icinga, I figured the intention was to call it check_all_disks_param. Therefore I updated it in this module.

Furthermore, the folks behind Icinga suggest using sysstat for monitoring certain resources (here: https://wiki.icinga.org/display/howtos/Monitoring+the+Icinga+Host ). The python script I used is one maintained by the maintainer of Icinga @dnsmichi .