Issue 50488 - Create a monitor for disk space usagedisk-space-mon
Description: Create a new monitor object: cn=disk space,cn=monitor.
It contains 'dsDisk' multi-valued attribute which has a format:
dsdisk: partition="/" size="42006183936" used="35768864768" available="6237319
168" use%="85"
dsdisk: partition="/tmp" size="1023303680" used="950198272" available="7310540
8" use%="92"
Add MonitorDiskSpace(DSLdapObject) to monitor.py.
Add a test to check the basic functionality.
Remove unused code and its statfs.h dependency.
Remove SLAPD_MONITOR_DN definition because it is unused.
https://pagure.io/389-ds-base/issue/50488
Authors: spichugi, mreynolds
Reviewed by: mreynolds, tbordaz, mhonek (Thanks!)