nemesis: introduce AbortRepair nemesis
nemesis: introduce AbortRepair nemesis

The new nemesis is used to test abort repair. It starts repair target_node
in background, wait until the repair starts, then try to abort the repair
streaming.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

amoskong/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,amoskong/scylla-cluster-tests,scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests