update zk tests

in the new version of nerve, the zookeeper nodes are sequential and do not have
well-defined names. we update the test to account for this. it will take the new
version of nerve to pass the test
nerve: bump version to 0.4.0
leader election service and tests

for the new synapse leader election functionality
synapse: new version

handles leader election, better node naming, and new docker code
Merge pull request #9 from airbnb/update_nerve_synapse

Update nerve and synapse