chore(server): set DefaultRemoveDelay to 30mins

Its value was 5s before, which could remove the node insanely fast.
Merge pull request #835 from unihorn/101

chore(server): set DefaultRemoveDelay to 30mins
fix(server): reduce the screaming heartbeat logs

Currently the only way we know that a peer isn't getting a heartbeat is
an edge triggered event from go raft on every missed heartbeat. This
means that we need to do some book keeping in order to do exponential
backoff.

The upside is that instead of screaming thousands of log lines before a
machine hits the default removal of 30 minutes it is only ~100.