Improve EFS mounting process

[giantcow]

Currently, when a new cluster is created, there will be 3-4 tasks that fail to start because they cannot mount EFS. Eg.:
Resourceinitializationerror: failed to invoke EFS utils commands to set up EFS volumes: stderr: Failed to resolve "fs-<id>.efs.us-east-1.amazonaws.com" - check that your file system ID is correct, and ensure that the VPC has an EFS mount target for this file system ID. See https://docs.aws.amazon.com/console/efs/mount-dns-name for more detail. Attempting to lookup mount target ip address using botocore. Failed to import necessary dependency botocore, please install botocore first. : unsuccessful EFS utils command execution; code: 1

• Only happens when a new EFS file system is created
• Cannot just add a delay, because then we'd artificially add delay when it would be working normally