sgcollect should pick up stderr output on all platforms

On panics inside goroutines that don't have explicit recover/logging handling, output will only end up going to stderr. sgcollect retrieves this on some platforms (included in syslog.tar.gz as messages on macos), but doesn't appear to do so on centos7 or later.

This appears to have better handling in cbcollect - need to review and port over to sgcollect as needed.