Distribute only functional and running bridges

Check if the ratio of functional or running bridges is good enough to only distribute those.

Use bridgestrap results to distribute only tested and functional resources. Unless the ratio of functional resources is too low, so rdsys keeps distributing resources after restarts (having most resources untested) or in case of bridgestrap failures.

When bridge authority restarts it might produce bridge descriptors without the running flag, as it hasn't tested the bridges yet. Let's ignore those updates.

Closes: #102 (closed) #96 (closed)