Fix three failing unittests in lib/bridgedb/Tests.py.

Three unittests were failing in lib/bridgedb/Tests.py due to changes made for
users). They were:

 - testDistWithFilterBoth (bridgedb.Tests.IPBridgeDistTests)
 - testDistWithFilterIP4 (bridgedb.Tests.IPBridgeDistTests)
 - testDistWithFilterIP6 (bridgedb.Tests.IPBridgeDistTests)

These were failing due to chopping the first 7 bytes off the the returned
config lines, because they expected to see the "bridge " prefix and it's not
there anymore.