bitbake: bb.data_smart: retain traceback from ExpansionError

This gives us the needed context of the original ExpansionError, which is
invaluable when we have a chain of function calls in the expansion.

(Bitbake rev: c514b6fbea77ede1b7871b89592a33ed39b1d71c)

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/data_smart.py

@@ -392,7 +392,8 @@ class DataSmart(MutableMapping):
             except bb.parse.SkipRecipe:
                 raise
             except Exception as exc:
-                raise ExpansionError(varname, s, exc)
+                exc_class, exc, tb = sys.exc_info()
+                raise ExpansionError, ExpansionError(varname, s, exc), tb
 
         varparse.value = s