mds: fix bug in MDCache::open_ino_finish

It's wrong to erase open_ino_info_t after finishing contexts, because
MDCache::open_ino() can be called again when finishing contexts.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: fix discover path race

When C_MDC_RetryDiscoverPath executed, we may have already become
auth mds of base

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>