ceph_pool: add idempotency to absent state

ceph_pool: add idempotency to absent state

When using the "absent" state on a non existing pool then the ceph_pool
module will fail and return a python traceback.

Instead we should check if the pool exit or not and execute the pool
deletion according to the result.
The state changed is now set when the pool is actually deleted.

This also disable add_file_common_args because we don't manipulate
files with this module.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>