Returns a string describing the package manager used by the target system.
This API call checks to see if the dpkg or rpm command exists on the system. If a system were to have both dpkg and rpm on the same system, the API will return dpkg since it is the first one checked.
DPKG if the system uses the DPKG package database.
RPM if the system uses the RPM package database.
Empty string if neither is found to be used.