tests: override XDG_RUNTIME_DIR where we use the user runtime dir

We don#t really support systems where XDG_RUNTIME_DIR is not supported for
systemd --user. Hence, let's always set our own XDG_RUNTIME_DIR for tests that
involve systemd --user, so that we know it is set, and that it doesn't polute
the user's actual runtime dir.

src/basic/rm-rf.h

@@ -30,3 +30,12 @@ typedef enum RemoveFlags {
 
 int rm_rf_children(int fd, RemoveFlags flags, struct stat *root_dev);
 int rm_rf(const char *path, RemoveFlags flags);
+
+/* Useful for usage with _cleanup_(), destroys a directory and frees the pointer */
+static inline void rm_rf_and_free(char *p) {
+        if (!p)
+                return;
+        (void) rm_rf(p, REMOVE_ROOT);
+        free(p);
+}
+DEFINE_TRIVIAL_CLEANUP_FUNC(char*, rm_rf_and_free);