cleanup: move is_systemd() inside ScyllaInstallGeneric
cleanup: move is_systemd() inside ScyllaInstallGeneric

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

scylladb/scylla-artifact-tests,scylladb/scylla-artifact-tests