Spark-3213 Fixes issue with spark-ec2 not detecting slaves created with "Launch More like this"

... copy the spark_cluster_tag from a spot instance requests over to the instances.

Author: Vida Ha <vida@databricks.com>

Closes #2163 from vidaha/vida/spark-3213 and squashes the following commits:

5070a70 [Vida Ha] Spark-3214 Fix issue with spark-ec2 not detecting slaves created with 'Launch More Like This' and using Spot Requests