EBS - Modify instance startup script to mount EBS volume, if required

The rc.local script will be modified to perform the following:

1. Execute a tool that
   1. Gets the instance user data from the EC2 web service (Already implemented)
   2. Extracts the EBS snapshot ID, AWS private key, certificate if supplied.
   3. If a snapshot id was found, create a new volume from it and attach it as /dev/sdh,
   4. If an unexpected error occurs, exits with return code 1.
   5. If no volume id was in the user data, exits with return code 2.
   6. If no valid user data was found, exits with return code 3. (Can be used to implement BAM-3107)
   7. Mount /dev/sdh as /mnt/bamboo-ebs
   8. If there is an executable file at /mnt/bamboo-data/bamboo-mount.sh, execute it.
2. Run the Elastic Agent.