Bug 2265: Modified NormalizedNodeOutputStreamWriter to implement yangtools interface

The NormalizedNodeOutputStreamWriter was originally written to implement
a NormalizedNodeStreamWriter interface class that was copied from
yangtools. This was done to get access to the NodeWithValue in the
leafSetEntryNode method which isn't specified in the yangtools
interface. However it turns out we don't actually need the NodeWithValue so
NormalizedNodeOutputStreamWriter was changed to implement the yangtols interface
and the copied NormalizedNodeStreamWriter interface was removed.

Change-Id: I72f0c96359e4fe96e8e183aa7afba9291c5d519d
Signed-off-by: tpantelis <tpanteli@brocade.com>
Merge "Bug 2265: Modified NormalizedNodeOutputStreamWriter to implement yangtools interface" into stable/helium