bitbake: command: Add missing import traceback

Without this, if an exception occurs the server will silently crash
with no feedback to the user about why (since traceback isn't imported).

(Bitbake rev: e637a635bf7b5a9a2e9dc20afc18aceec98d578f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/command.py

@@ -69,6 +69,7 @@ class Command:
             except CommandError as exc:
                 return None, exc.args[0]
             except Exception:
+                import traceback
                 return None, traceback.format_exc()
             else:
                 return result, None