reset sendIndex on sync failure
Cleaned log message.

- Poll failed with Exception case
Replication bug fixes

Conflicts:
	core/src/main/java/net/kuujo/copycat/internal/replication/NodeReplicator.java
When a server becomes the leader, the first log entry it should apply must be the greater of context.lastApplied + 1 and log.firstIndex
This takes care of the case where the server has previously compacted the log and therefore its log's first index is no longer 1