bitbake/bitbake-runtask: Signatures are needed in task context and have little overhead so enable in worker context

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/bin/bitbake-runtask

@@ -20,6 +20,7 @@ class BBConfiguration(object):
         setattr(self, "data", {})
         setattr(self, "file", [])
         setattr(self, "cmd", None)
+        setattr(self, "dump_signatures", True)
 
 _warnings_showwarning = warnings.showwarning
 def _showwarning(message, category, filename, lineno, file=None, line=None):