objclass: change objclass exec read calls to write ones where needed

objclass: change objclass exec read calls to write ones where needed

Many of the exec calls were using a read version of the API while they
were calling a write objclass method. This modifies the calls to use
the write API.

Fixes: https://tracker.ceph.com/issues/65889
Signed-off-by: Yehuda Sadeh <ysadehwe@ibm.com>