add_nodes: assign bootstrap argument referencing to enable_auto_bootstrap parameter
add_nodes: assign bootstrap argument referencing to enable_auto_bootstrap parameter

We had added a parameter (enable_auto_bootstrap) for add_nodes() function,
but we still have some logic to decide the bootstrap value inside add_nodes().
We should directly assign bootstrap argument in ec2_user_data referencing the
`enable_auto_bootstrap` parameter.

This problem was reported by Yakovlev Julia.

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

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