SeverityType has levels which do not seem to follow convention for log levels

[rodrigc]

In: https://github.com/libopenstorage/openstorage/blob/master/api/api.proto#L68

we have this:

enum SeverityType {
  SEVERITY_TYPE_NONE = 0;
  SEVERITY_TYPE_ALARM = 1;
  SEVERITY_TYPE_WARNING = 2;
  SEVERITY_TYPE_NOTIFY = 3;
}

If I look at the default log levels in the Python standard library (CRITICAL, ERROR, WARNING, INFO, DEBUG, NOTSET): https://docs.python.org/3/library/logging.html#logging-levels

and in this Go library:

https://github.com/op/go-logging/blob/master/level.go#L20

libopenstorage does not seem to follow this convention for log levels.

If possible, I would suggest that it would be good to follow the convention for log levels established elsewhere. A lot of third party log tools follow these conventions.