test: Use log_setup()

Specifically, this will make tests log to the journal if stderr is
connected to the journal. This means we get proper log priorities
and such compared to if we just logged to stderr.

src/shared/tests.c

@@ -116,8 +116,7 @@ bool slow_tests_enabled(void) {
 void test_setup_logging(int level) {
         log_set_assert_return_is_critical(true);
         log_set_max_level(level);
-        log_parse_environment();
-        log_open();
+        log_setup();
 }
 
 int write_tmpfile(char *pattern, const char *contents) {