bitbake: data_smart: Add original traceback to ExpansionError

This can make it print clearer errors, for exmaple:

Add Runtime_error to 'def oe_import(d)"

 16 def oe_import(d):
 17     import sys
 18     Runtime_error
[snip]

* Before the patch:
  $ bitbake -p
  ERROR: Unable to parse /buildarea1/lyang1/poky/bitbake/lib/bb/data_smart.py
  Traceback (most recent call last):
    File "/buildarea1/lyang1/poky/bitbake/lib/bb/data_smart.py", line 430, in DataSmart.expandWithRefs(s='${@oe_import(d)}', varname='OE_IMPORTED[:=]'):
                   except Exception as exc:
      >                raise ExpansionError(varname, s, exc) from exc

  bb.data_smart.ExpansionError: Failure expanding variable OE_IMPORTED[:=], expression was ${@oe_import(d)} which triggered exception NameError: name 'Runtime_error' is not defined

  This error message has two problems:
  - "Unable to parse data_smart.py": This isn't the real cause.
  - It pionts to "raise ExpansionError(varname, s, exc) from exc" which isn't clear enough.

* After the patch:
  $ bitbake -p
  ERROR: Unable to parse OE_IMPORTED[:=]
  Traceback (most recent call last):
    File "OE_IMPORTED[:=]", line 1, in <module>
    File "/buildarea1/lyang1/poky/meta/classes/base.bbclass", line 18, in oe_import(d=<bb.data_smart.DataSmart object at 0x7f9257e7a0b8>):
           import sys
      >    Runtime_error

  bb.data_smart.ExpansionError: Failure expanding variable OE_IMPORTED[:=], expression was ${@oe_import(d)} which triggered exception NameError: name 'Runtime_error' is not defined

This one is more clearer than before.

(Bitbake rev: c0fe524c1aeccb24ddd2e1f7bf235c00fdbf79a7)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/data_smart.py

@@ -427,7 +427,8 @@ class DataSmart(MutableMapping):
             except bb.parse.SkipRecipe:
                 raise
             except Exception as exc:
-                raise ExpansionError(varname, s, exc) from exc
+                tb = sys.exc_info()[2]
+                raise ExpansionError(varname, s, exc).with_traceback(tb) from exc
 
         varparse.value = s