make exception handling syntax consistent

Update exception handling syntax to use the modern style:
except ExcType as localvar

(Bitbake rev: dbf5f42b06bef81749b13aa99945cc1292a6676d)

Signed-off-by: Scott Garman <scott.a.garman@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake

@@ -32,7 +32,7 @@ import warnings
 from traceback import format_exception
 try:
     import bb
-except RuntimeError, exc:
+except RuntimeError as exc:
     sys.exit(str(exc))
 from bb import event
 import bb.msg