memtx: fix a bug with insertion to space during recovery

There was a problem whith on_schema_init trigger.
This trigger gives a way to create on_replace trigger
that will modify temporary or is_local spaces during recovery
from snapshot, but on that stage of recovery process
all space indexes are in special build mode when no check
for uniqueness are made. I added a new function
'is_recovery_finished' in box.ctl, which gives
user ability to check that we are in snapshot recovery stage
and can't insert/replace/update/upsert something. Also i added a
check for corresponding operations, now they are failed
if user tries to do them during snapshot recovery.

@TarantoolBot document
Title: Add 'is_recovery_finished' function
Add 'is_recovery_finished' function in box.ctl
to add user ability to check that we are
in snapshot recovery stage and can't
insert/replace/update/upsert something

Closes #5304