improve FetchError message

bin/varnishd/cache/cache_fetch.c

@@ -537,7 +537,7 @@ vbf_fetch_body_helper(struct busyobj *bo)
 #define vbf_vfp_push(bo, vfp, top)					\
 	if (VFP_Push((bo)->vfc, (vfp), (top)) == NULL) {		\
 		assert (WS_Overflowed((bo)->vfc->http->ws));		\
-		(void)VFP_Error((bo)->vfc, "Bo workspace overflowed");	\
+		(void)VFP_Error((bo)->vfc, "workspace_backend overflow"); \
 		(bo)->htc->doclose = SC_OVERLOAD;			\
 		VDI_Finish((bo)->wrk, bo);				\
 		return (F_STP_ERROR);					\

bin/varnishtest/tests/r01739.vtc

@@ -16,7 +16,7 @@ varnish v1 \
 } -start
 
 logexpect l1 -v v1 -g raw {
-	expect * 1002 FetchError {^Bo workspace overflowed}
+	expect * 1002 FetchError {^workspace_backend overflow}
 	expect * =    Error      {^out of workspace [(]Bo[)]}
 } -start