Bug 7449: Add message slicing/re-assembly classes

Bug 7449: Add message slicing/re-assembly classes

Added re-usable classes for slicing messages into smaller chunks and
re-assembling them. The process is similar to the current raft
install snapshot chunking.

The 2 main classes are MessageSlicer and MessageAssembler. The basic workflow
is:

 - MessageSlicer#slice method is called which serializes the message,
   creates and caches a SlicedMessageState instance and determines the number
   of slices based on the serialized size and the maximum message slice size,
   then sends the first MessageSlice message.
 - The MessageAssembler on the other end receives the MessageSlice, creates an
   AssembledMessageState instance if necessary and appends the byte[] chunk to
   the assembled stream. A MessageSliceReply is returned.
 - The MessageSlicer receives the MessageSliceReply and sends the next
   MessageSlice chunk, if necessary.
 - Once the last MessageSlice chunk is received by the MessageAssembler, it
   re-assembles the original message by de-serializing the assembled stream
   and notifies the user-supplied callback (of type Consumer<Object>) to handle
   the message.

Both MessageSlicer and MessageAssembler use a guava Cache and can be configured
to evict state that has been inactive for a period of time, ie if a message hasn't
been received by the other end.

The MessageSliceReply can propagate a MessageSliceException. If the
MessageSliceException indicates it's re-triable, the MessageSlicer will restart
slicing from the beginning. Otherwise slicing is aborted and the user-supplied
failure callback is notified.

Change-Id: Iceea212b12f49c3944bade50afded92244e4b31a
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>