Added the ability to specify heartbeat and election timeouts as config parameters.

As penance for my twitter-whine, this is a small patch (my first bit of Go hackery, which will explain a lot), which allows the network timeouts to be specifiable as command line parameters (-peer-heartbeat-timeout and -peer-election-timeout). The defaults are the same as were coded in server/timeout.go

Note: I've only tried this on a 3 way cluster, between 2 joyent and 1 ec2 nodes, in the us-west, us-east and eu-ams regions. Which means that it will need much better checking out to see what other damage I've done.

Note: the Dockerfile change was for my personal config setups, so shouldn't really be in here, tbh.