BUG-944: convert SchemaContextUtil to use Iterable

SchemaContextUtil is heavily centered around the idea that a SchemaPath
has a List of QName. That assumption is deprecated, so convert this
class to use Iterable instead, preparing it for transition to new APIs.

Change-Id: I0e23bd534c441d19aab62eb7a3069244b27532b2
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-944: convert SchemaContextUtil to use Iterable"