LU-3203 mdd: check result of dt_trans_create() using IS_ERR().

LU-3203 mdd: check result of dt_trans_create() using IS_ERR().

In mdd_convert_linkea() and orphan_object_destroy() check the result
of dt_trans_create() using IS_ERR().  In mdd_close() avoid passing an
error pointer to mdd_trans_stop().  In local_oid_storage_init() avoid
a spurious mutex unlock after failure in dt_trans_create().  Trivially
simplify cleanup in mdd_convert_remove_dots() and mdd_convert_lma().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I4a5c53d3efa9c69c1428a8e5a875a531c9206d12
Reviewed-on: http://review.whamcloud.com/6117
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>