Bug 5485: Improve DataTreeModification pruning on recovery

Modified the PruningDataTreeModification and NormalizedNodePruner to
validate path and node QNames via the SchemaContext instead of just
namespaces. This allows migration support for any element to be removed
from a yang hierarchy.

Also handled SchemaValidationFailedException on ready which can happen
with writes which don't immediately validate the sctructure as merge
does. The modification tree is re-applied with pruning.

Change-Id: I8c4f84fbaa93563ce6741d7a3e15855f7fc4940f
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>