Enhance diagnostic information when a room connection fails

[MarkNSweep]

When connections to room fail or cannot be started, need to output more diagnostic information so that the root cause can be established - rather than 'connection failed'.

[ebullient]

A) If we have the information
B) Some may be better served in the UI (for room owner) than in the mediator
C) Data should not be exposed back through UI (which means only visible in mediator logs, which is of mixed utility to anyone but us)