Bug 2156: Unsupported augment target

Some yang models contain augmentations into unsupported target
(e.g. node in body of extension). This causes maven build failure
(by generation of DTO), even though parsing such models is successful.

Change-Id: I8efff696aa2d3b95c5168ba8e42d49a93d1dff74
Signed-off-by: pkajsa <pkajsa@cisco.com>
(cherry picked from commit 48387f2188ee83a3c8e909df01e109ebd3e7c89c)
Merge "Bug 2156: Unsupported augment target" into stable/helium