LU-5020 llite: don't reconnect MGC if connecting

1. In mgc_set_info_async(KEY=KEY_INIT_RECOV_BACKUP "init_recov_bk"),
   the MGC import should be reconnected only if its state is
   LUSTRE_IMP_DISCON

2. in mgc_target_register, if the target will regenerate the config,
   we should use some longer delay limit to wait the MGC to connect
   to MGS for the target (server) will fail to exit if the request
   expired due to delay limit.

3. In case of parallel mount, the async cleanup of OSS will affects
   the following mount for the OSS can't be setup again, then there
   should be some barrier to sync with the OSS cleanup.

Change-Id: I805b84cf12100ec2cc68f95bb65a9c396e0fbc1b
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: https://review.whamcloud.com/10229


Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>