Don't fail if MongoDB is not available
Use mongodb_uri string to connect to the DB

This is more flexible than using host and port. For example
using this syntax we can also supply the username and password
for connecting to the DB. We can even connect to a MongoDB
Replica Set (aka cluster) this way.
Log erors and be robust in the request method
Save those requests that never actually made it
Merge pull request #2 from redbeacon/feature-high-availability

Feature high availability