Reduce the default FD timeout in JGroups stacks

The default FD timeout of 50 secs can introduce prolonged cluster disruptions in scenarios where FD_SOCK doesn't detect a failure immediately. With OOB in the 2.6+ JGroups that AS 5 will use, the problem of FD responses getting stuck behind regular messages is gone, so we can be somewhat more aggressive with the default. Will change to 30 seconds.

Will not apply this to the 4.x series, where OOB doesn't exist.