Allow for configurable LWT CL

[rustyrazorblade]

First, for context, updating running repairs uses a SERIAL consistency level:

setRunningRepairsPrepStmt = session
        .prepare(
            "UPDATE running_repairs USING TTL ?"
                + " SET reaper_instance_host = ?, reaper_instance_id = ?, segment_id = ?"
                + " WHERE repair_id = ? AND node = ? IF reaper_instance_id = ?")
        .setSerialConsistencyLevel(ConsistencyLevel.SERIAL)
        .setConsistencyLevel(ConsistencyLevel.QUORUM)
        .setIdempotent(false);

In a deployment with multiple datacenters, this is used to ensure multiple reaper instances don't stomp all over each other. However, if you're running a single reaper out of 1 DC and using it to coordinate, it's unnecessary. Normally, I'd just recommend confining the reaper keyspace to a single DC to avoid the problem, but when using k8ssandra, it forces you to use a multi-dc setup and I'm finding LWTs are constantly timing out.

This issue to make Reaper configurable to be able to use ConsistenyLevel.LOCAL_SERIAL.

┆Issue is synchronized with this Jira Story by Unito
┆Issue Number: REAP-199