Optimize write call add enhance error detect

A single write call may need several keys in the backend kv store. Let get these
keys one time.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
Remove unnecessary "check_coll" check

The goal of "check_coll" is aimed to ensure the collection is exists. But
the create and delete of collection already ensured by OSD, just remove check.

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>