tests: Silence gtester in Makefile

This prettifies make output a little by avoiding a very long line.
As gtester prints the checks when they are run, no information is lost.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

tests/Makefile

@@ -36,4 +36,4 @@ test-qmp-commands: test-qmp-commands.o $(qobject-obj-y) $(qapi-obj-y) $(tools-ob
 
 .PHONY: check
 check: $(CHECKS)
-	gtester $(CHECKS)
+	$(call quiet-command, gtester $(CHECKS), "  CHECK")