Do not pass NoneType as argument to ceph_crush_rule

Do not pass NoneType as argument to ceph_crush_rule

With ansible-core 2.15 it is not possible to pass argument of unexpected
type, as otherwise module will fail with:
`'None' is not a string and conversion is not allowed`

With that we want to only get all existing crush rules, so we can simply
supply an empty string as a name argument, which would satisfy
requirements and have same behaviour for previous ansible versions.

Alternative approach would be to stop making `name` as a required
argument to the module and use empty string as default value
when info state is used.

Signed-off-by: Dmitriy Rabotyagov <noonedeadpunk@gmail.com>