Bug 1224, Bug 1221: Added Test case scenarios for Data Change Events.

Added suite of test-cases which tests Data Change Events
and their contents for various combination of
  - initial state of data store
  - performed operation (e.g. write sibling, child, delete child)
  - various level of data change listener
    eg. (/top or /top/top-level-list/top-level-list[*])
  - various data change scope (BASE, ONE, SUBTREE)

Change-Id: Ic43ba3863e2954574ddec946f33512021839acfd
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>