LU-5370 mdt: return -MDT_EREMOTE_OPEN for remote open

LU-5370 mdt: return -MDT_EREMOTE_OPEN for remote open

Add a special magical errno MDT_EREMOTE_OPEN for communicaiton between
mdt_reint_open() and mdt_intent_reint() which means return the lock to
the client for subsequent cross ref open. Previously we used plain
-EREMOTE but other functions called in that path might return it too
and confuse us. This is not returned to the client.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I7a498adc341c2b52b29c94f65e66431c5de06917
Reviewed-on: http://review.whamcloud.com/11218
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>