Allow disabling `curl` command for Storm clusters

This partially addresses https://github.com/viki-org/storm-docker/issues/1

Disabling the running of the `curl` command is done by setting the
`all_machines_are_ec2_instances` field in the `config/storm-setup.yaml`
file to False or omitting the field.

Signed-off-by: Pang Yan Han <yanhan@viki.com>