bugfixes

bugfixes

- Fix do_mount_cgroups(): It previously returned ret uninitialized on failure.
- Quite a few snprintf() call used size_t variables but then checked whether
  size_t < 0. Since size_t is unsigned these checks were always true. Let's use
  ssize_t instead which is signed.
- Use additional ssize_t variable to catch snprintf() error for swap
  calculation and add the value to the final result afterwards instead of
  directly.

Signed-off-by: Christian Brauner <christian.brauner@mailbox.org>