[dovecot/core] 69a993: dsync: Fix .dovecot-sync.lock timeout checking

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 69a9934b56438719c9eed2ca876b08a4ff445dd7
      https://github.com/dovecot/core/commit/69a9934b56438719c9eed2ca876b08a4ff445dd7
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2016-12-12 (Mon, 12 Dec 2016)

  Changed paths:
    M src/doveadm/dsync/dsync-brain.c

  Log Message:
  -----------
  dsync: Fix .dovecot-sync.lock timeout checking

Whenever the lock file was recreated, the lock timeout was reset. Switched
to using file_create_locked(), which already solves this problem and has
compatible locking.