RHEL 7 で firewalld サービスが失敗し起動しない

Issue

• 以下のように firewalld が起動できません。

  # systemctl restart firewalld.service
  Job for firewalld.service failed.See 'systemctl status firewalld.service' and 'journalctl -xn' for details.
  

• 以下のログは、失敗した firewalld サービスの詳細を提供しています。

  # systemctl status firewalld.service -l
  firewalld.service - firewalld - dynamic firewall daemon
     Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
     Active: failed (Result: timeout) since Mon 2014-07-07 13:49:26 BST; 7min ago
   Main PID:20708
  
  Jul 07 13:47:55 HOSTNAME systemd[1]:Starting firewalld - dynamic firewall daemon...
  Jul 07 13:49:25 HOSTNAME systemd[1]: firewalld.service operation timed out.Terminating.
  Jul 07 13:49:26 HOSTNAME systemd[1]:Failed to start firewalld - dynamic firewall daemon.
  Jul 07 13:49:26 HOSTNAME systemd[1]:Unit firewalld.service entered failed state.
  
  # journalctl -xn
  -- Logs begin at Fri 2014-06-13 19:52:40 BST, end at Mon 2014-07-07 13:50:01 BST
  Jul 07 13:47:55 HOSTNAME kernel: nf_conntrack version 0.5.0 (16384 buckets, 6
  Jul 07 13:47:55 HOSTNAME kernel: ip6_tables:(C) 2000-2006 Netfilter Core Tea
  Jul 07 13:47:55 HOSTNAME kernel:Ebtables v2.0 registered
  Jul 07 13:49:25 HOSTNAME systemd[1]: firewalld.service operation timed out.T
  Jul 07 13:49:26 HOSTNAME kernel:Ebtables v2.0 unregistered
  Jul 07 13:49:26 HOSTNAME systemd[1]:Failed to start firewalld - dynamic fire
  -- Subject:Unit firewalld.service has failed
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  --
  -- Unit firewalld.service has failed.
  --
  -- The result is failed.
  Jul 07 13:49:26 HOSTNAME systemd[1]:Unit firewalld.service entered failed st
  Jul 07 13:50:01 HOSTNAME systemd[1]:Starting Session 4064 of user root.
  -- Subject:Unit session-4064.scope has begun with start-up
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  --
  -- Unit session-4064.scope has begun starting up.
  Jul 07 13:50:01 HOSTNAME systemd[1]:Started Session 4064 of user root.
  -- Subject:Unit session-4064.scope has finished start-up
  lines 1-23
  

• このような firewalld エラーを発生させているのは何ですか?
• 以前、システムで Docker が使用され、設定されていました。docker を停止したあとに firewalld サービスを起動しようとすると、上述のエラーが発生します。