size-rotating-file-handler rotate-size doens't properly handle add/update with management API

From the management API, rotate-size doesn't handle the one-character suffixes for (b)yte, (k)ilobyte, (m)egabyte, etc.

So for instance, if you say:
/subsystem=logging/size-rotating-file-handler=SIZE:update-properties(rotate-size=5m)

You will get an error because it will try to convert that to a long. If you enter a valid long without a suffix, then the value will be corrupted when the server is restarted.

The solution is to keep this attribute as a String in the management model and only parse out the suffix when you need to convert to a long for the runtime.