RF values appear as strings and strategies classes convert them to integers. This PR removes some duplication of efforts in converting code.
Closesscylladb/scylladb#17132
* github.com:scylladb/scylladb:
network_topology_strategy: Do not walk list of datacenters twice
replication_strategy: Do not convert string RF into int twise
abstract_replication_strategy: Make validate_replication_factor return value