BUG-994: do not use SchemaPath.getPath()

SchemaContextUtil used getPath() to construct parent from the path --
use getParent() instead. Furthermore convert uses where it is only used
as Iterable into getPathFromRoot().

Change-Id: I455e9e297c4ed6a7f861bb6cc9b6e4ece2bd8337
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-994: do not use SchemaPath.getPath()"