Missing metadata type for snmp diskio pollsters

[Tom Carroll]

Version: stable/rocky and HEAD

The hardware.disk.read|write.* stats are defined with metadata with an unspecified type. When polling for hardware.disk.read.bytes, ceilometer-central-agent reports:

2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic [-] inspector call failed for hardware.disk.read.bytes host compute0.example.com: 'type': KeyError: 'type'
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic Traceback (most recent call last):
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic File "/usr/lib/python2.7/dist-packages/ceilometer/hardware/pollsters/generic.py", line 149, in get_samples
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic inspector_param = ins.prepare_params(param)
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic File "/usr/lib/python2.7/dist-packages/ceilometer/hardware/inspector/snmp.py", line 345, in prepare_params
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic processed['metadata'][k] = (v['oid'], eval(v['type']))
2018-12-13 11:35:19.152 1232 ERROR ceilometer.hardware.pollsters.generic KeyError: 'type'

A patch is attached that adds the "type" attribute.