Add more aggressive retry schedule for failed bridges

In an effort to address better handling of gone resources for Lox's purposes, this commit introduces a more aggressive retry schedule for bridges that fail bridgestrap's test. For now, the error timeout can be set so bridges that fail a test are only cached for x (default 1) hour(s). Follow up work on rdsys (and adding similar functionality for onbasca tests) to follow. This also addresses #29 (closed)