Make MANAGER_TEST_RUN_MINIMAL just allocate data structures

When running tests like test-unit-name, there is not point in setting
up the cgroup and signals and interacting with the environment. Similarly
when running fuzz testing of the parser.

Add new MANAGER_TEST_RUN_BASIC which takes the role of MANAGER_TEST_RUN_MINIMAL,
and redefine MANAGER_TEST_RUN_MINIMAL to just create the basic data structures.

src/test/test-engine.c

@@ -47,7 +47,7 @@ int main(int argc, char *argv[]) {
         /* prepare the test */
         assert_se(set_unit_path(get_testdata_dir("")) >= 0);
         assert_se(runtime_dir = setup_fake_runtime_dir());
-        r = manager_new(UNIT_FILE_USER, MANAGER_TEST_RUN_MINIMAL, &m);
+        r = manager_new(UNIT_FILE_USER, MANAGER_TEST_RUN_BASIC, &m);
         if (MANAGER_SKIP_TEST(r)) {
                 log_notice_errno(r, "Skipping test: manager_new: %m");
                 return EXIT_TEST_SKIP;