Pass just Request field to PreProcessor instead of whole request object.
Merge pull request #65 from EasonLiao/fix_preprocessor

Pass just Request field to PreProcessor instead of whole request object.
Merge pull request #61 from EasonLiao/failure_cases

Some more failure cases.
refactor: SimpleLog.java
Merge pull request #66 from fengjingchao/master

refactor: SimpleLog.java
Switch QuorumZab to Netty transport.
Merge pull request #67 from EasonLiao/netty_zab

Switch QuorumZab to Netty transport.
Fixed small bug and added shutdown to QuorumZab.
Print out number of active threads before/after each test.
Merge pull request #73 from EasonLiao/netty_zab

Fixed small bug and added shutdown to QuorumZab.
Clean up logging.

Some information became redundant since we started using MDC.
Merge pull request #79 from m1ch1/logging

Clean up logging.
netty transport cleanup.

- Remove unused close() method.
- Don't clear the senders map from the shutdown method. Instead, let
  the ErrorHandler do the clean up.
- Don't print stack trace for connection failed error.
- Add a comment and some asserts around handling disconnect.
Merge pull request #81 from m1ch1/netty

netty transport cleanup.
Delete SingleNodeZab.

Now we can use leader-only QuorumZab instead of SingleNodeZab.
Merge pull request #82 from m1ch1/master

Delete SingleNodeZab.
Transport: make the caller acknowledge the onDisconnected event.

Since the onDisconnected callback is invoked from a netty thread,
it's easy for the caller to get reconnected without realizing that
it has been disconnected.

With this patch, the transport stops sending/receiving messages
to/from the destination once the onDisconnected callback is invoked.
To reestablish the connection, the caller must explicitly call the
clear() method.
NettyTransport: remove tie breaker logic.

With this patch, the handshake fails if there is a tie and the caller
gets the onDisconnected event. It's up to the caller to call the
clear() method and re-initiate the handshake, adding some sort of
back-off logic if necessary.
NettyTransport: remove handshake retry logic.
Merge pull request #83 from m1ch1/master

transport cleanup.