ETCH-278 Enable receiving of multiple packages in one buffer in EtchPackizer

Till now the packetizer was not able to handle more then one packet in a
buffer received from the transport layer.
This patches introduces a new algorithm to handle packets and adds tests
to ensure it works for all possible situations.

Change-Id: I7ba4b04a012ed8778861dc734ba2574d2b487ac9

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1579568 13f79535-47bb-0310-9956-ffa450edef68