Fix startup-crasher and simplify timeout handling.

* cgmanager-proxy.c:
  - setup_proxy(): Adding missing return -1.
  - main(): Ensure setup is complete before accepting connections
    (crasher).
* frontend.c:
  - timer_cmp_fn(): Return whole range of expected values.
  - timeout_remove(): Simplify.
  - timeout_reset(): Simplify.
  - timeout_add(): Use nih_alloc_set_destructor() for simplicity.

Signed-off-by: James Hunt <james.hunt@ubuntu.com>