tests: adapt test_zone-update to work on 32 bit architectures

The test might fail on 32 architectures with error message claiming
"not enough memory". This is probably caused by address space
fragmentation.

To avoid this problem we are using pretty low values for database size
in the test (which contains little data anyway).

tests/test_zone-update.c

@@ -293,6 +293,7 @@ int main(int argc, char *argv[])
 	         " - domain: test.\n"
 	         "template:\n"
 	         " - id: default\n"
+		 "   max-journal-db-size: 100M\n"
 	         "   storage: %s\n",
 	         temp_dir);