LU-598 open non-exist object should return ENOENT

LU-598 open non-exist object should return ENOENT

When call ll_intent_file_open() against non-exist object, we cannot
obtain RPC request refcount after the call, so subsequent operation
should not use such internal (only) RPC request to avoid to access
freed (or re-allocated) memory.

Change-Id: I4c3763f460c6145e376538f392fde338d44e6c5e
Signed-off-by: nasf <yong.fan@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1242
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>