As a user I want to use spot functionality during Spark cluster creation so that I can reduce financial charges on AWS/GCP/MS Azure.
1. it should be check box for spot instance on Spark cluster creation popup
2. check box for Low spot instance should be checked off by default
3. if user unchecks check box for spot instance and hits 'Create' button a Spark cluster will be created without spot price
4. if user checks off check box for spot instance and hits 'Create' button a Spark cluster will be created with spot price
Github issue: https://github.com/apache/incubator-dlab/issues/742