Support mocking of obfs4 transports in bridge-extrainfo descriptors.
Support mocking of obfs4 transports in bridge-extrainfo descriptors.

 * FIXES part of #12932 (or at least allows BridgeDB to have regression
   tests for #12932). See https://bugs.torproject.org/12932.

isislovecruft/leekspin,isislovecruft/leekspin