This PR fixes a bug where the mina daemon would not acquire the daemon lockfile
(the `.mina-lock` file in the daemon config directory) after it had deleted a
stale lockfile left over from a crashed or killed daemon. Daemons must always
acquire this lockfile before continuing startup, since it is used, for instance,
to prevent multiple daemons from starting up in the same config directory and
potentially interfering with each other.
