use GetShortSourceTypeName from loggregatorlib

[oppegard]

We added the following method to loggregatorlib:

https://github.com/cloudfoundry/loggregatorlib/blob/master/logmessage/message.go#L26

Which was cribbed from the cli:

https://github.com/cloudfoundry/cli/blob/master/src/cf/commands/application/helpers.go?source=c#L93

It'd be nice to use the loggregatorlib version so the same "short name" is used everywhere.

[dam5s]

I think this was added to our icebox/backlog, if not I'll make sure it is.

[scottruitt]

I put it in our backlog for the IPM.

[scottruitt]

Done. Thanks, Glenn.