WSUG: Convert ``Troubleshooting'' to AsciiDoc.

The chapter is disabled so its final output hasn't been checked. Leave
most of the content intact for now.

Change-Id: I2147ee2863e7ededadf892794a836b4dc8055649
Reviewed-on: https://code.wireshark.org/review/5211
Reviewed-by: Gerald Combs <gerald@wireshark.org>