Reachability tests for obfuscated bridges

Bridge authorities are supposed to do reachability tests to bridges.

This becomes problematic when pluggable transports are deployed since the bridge authority will need a pluggable transport to properly communicate with an obfuscated bridge.

Here are some solutions:

a) All the pluggable transports of a bridge will be considered reachable if the ORPort of the bridge is reachable.

b) The above + a TCP scan on each transport port to make sure that the port is open.

c) The bridge authority supports many the known and widely used pluggable transports and does robust reachability tests on all the transport ports. When it does not recognize a transport, it falls back to a) or b).

As part of legacy/trac#4568 (moved) it was decided to go with a) for now. In the future, we should probably drift towards c) since it seems to be the right thing to do (Thandy deployment would also make it a bit easier).

Any ahas, opinions, thoughts or possible solutions?