raft leader transition log not helpful

[bcwaldon]

Today, when a cluster comes up, it logs something like this:

2014/10/28 08:46:36 raft: leader changed from 0 to 2a567253ac2a647d

Since I am close to the project, I know that this means that there was no leader in the cluster, but now the leader has the ID 2a567253ac2a647d.

However, as an operator with no specific knowledge of how the code is written, that 0 might be a red flag. It looks like there was a leader with ID 0.

We should present this transition differently, so it's clear that there legitimately was no leader. Maybe we use the following:

cluster %x elected leader %x
cluster %x leader changed from %x to %x
cluster %x leader lost

[xiang90]

I will improve this.