mds: don't create bloom filter for incomplete dir

mds: don't create bloom filter for incomplete dir

Creating bloom filter for incomplete dir that was added by log
replay will confuse subsequent dir lookup and can create null
dentry for existing file. The erroneous null dentry confuses the
fragstat accounting and causes undeletable empty directory.

The fix is check if the dir is complete before creating the bloom
filter. For the MDCache::trim_non_auth{,_subtree} cases, just do
not call CDir::add_to_bloom because bloom filter is useless for
replica.

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