tests: valgrind: do not trace system binaries

Add /usr/bin/* to -trace-children-skip
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

tests/Makefile.am

@@ -485,7 +485,7 @@ TESTS_ENVIRONMENT = \
 
 
 VALGRIND = valgrind --quiet --leak-check=full --trace-children=yes \
-	--trace-children-skip="*/tools/virsh","*/tests/commandhelper" \
+	--trace-children-skip="*/tools/virsh","*/tests/commandhelper","/usr/bin/*" \
 	--suppressions=$(abs_srcdir)/.valgrind.supp
 valgrind:
 	$(MAKE) check VG="$(LIBTOOL) --mode=execute $(VALGRIND)"