Add const manubulonPluginDir definition

refs #6650

Signed-off-by: Gerd von Egidy <gerd@egidy.de>
Add some manubulon snmp plugins

refs #6650

Signed-off-by: Gerd von Egidy <gerd@egidy.de>
Add documentation for manubulon snmp plugins

refs #6650

Signed-off-by: Gerd von Egidy <gerd@egidy.de>