improve the error messages when invalid declarative jobsets are defined

(cherry picked from commit 7568b89a1a9da3a58a0cdddc7b5bcea7bb6209d8)

Created by  Michael Bishop  on September 11, 2018
HEZQ273SDMUIQFI3YWPDNSSIOYRFT3KWPOKCDCBYATBMGPLU4F6AC
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