Add MegaCLI collector

This collector exports the following metrics:

- raid_drive_temperature: drive temperature
- raid_drive_count: drive error and event counters
- raid_adapter_disk_presence: disk presence per adapter

collector/collector.go

@@ -18,5 +18,6 @@ type Collector interface {
 // time.)
 
 type Config struct {
+	Config     map[string]string `json:"config"`
 	Attributes map[string]string `json:"attributes"`
 }