rest-api: change name validation on update and tests for same

This allows name to be present on an update, and still rejects updating
a pool to have the same name as another pool

Signed-off-by: Gregory Meno <gmeno@redhat.com>

Fixes: #9522
Merge pull request #213 from ceph/wip-9522

rest-api: change name validation on update and tests for same