If we see errors during parsing, firstly its bad to show a traceback
for an expansion error so lets suppress this.
Secondly, raise a BBHandledException instead of a SystemExit to show
we've informed the user about the condition (printing a traceback in the
default unknown case).
(Bitbake rev: e01988d9a1b7c40e31161c6ce7b85c4405671068)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>