Rework the SNMP collector script snmp_getdata.py

[dupremathieu]

The SNMP collector script snmp_getdata.py have some hardcoded disk node path (e.g. /dev/sda).

We should modify it to support NVME disk.

I also suggest changing the title from smartctl /dev/sd# to a generic smartctl disk#.

The other issue we have in this script is that smartctl can require the -d argument to work. It is the case when you have a RAID controller, for instance.

The latest problem is that the SNMP should work on standalone and observer machines, so the clustering and virtualization monitoring should be done only if we have the virtualization or the cluster enabled.