Makefile: improve [make test] to use more parallelism and produce interactive output.

Makefile

@@ -59,11 +59,12 @@ clean:
 # toplevel, then we run [make unattended_norebuild] in every demo directory.
 
 # LOOP := xargs -n1
-LOOP := parallel --no-notice --jobs 4
+LOOP := parallel --no-notice --jobs 8 --group
 
 .PHONY: test
-test: dependencies
-	@ make clean
+test:
+#	@ make dependencies
+#	@ make clean
 	@ make -f Makefile.monolith all --no-print-directory
 	@ $(DEMOS) \
 	  | $(LOOP) make unattended_norebuild --no-print-directory -C