Log when node up/down events occur

This is a cherry-pick of:

https://github.com/cloudant/couch_replicator/commit/d40bb6f2e603a7c81f777cc1c4c200ad34c3db42
1 file changed
tree: c33c418d90c33d9b14fd1f53384ae13534f86e23
  1. priv/
  2. src/
  3. test/
  4. .gitignore