2-DC cluster parallel non-RBNO rebuild failure when expanding RF in DC2.
Steps to reproduce:
1. Provision a cluster with 2 datacenters and at least 2 nodes in the second datacenter.
2. Let’s assume datacenter names are "dc1" and "dc2".
3. Create a keyspace ("keyspace1") with RF=0 in dc2.
4. Populate some data into dc1.
5. Change keyspace1 replication in dc2 to 2.
6. On 2 nodes in dc2 run the following command in parallel:
nodetool rebuild --source-dc dc1
Parallel execution of rebuilds is not possible with RBNO enabled.
This test is the repro for #27804Closesscylladb/scylladb#27747