Add disk statistics for remote EC2 instances

We are able to periodically collect system and process information, using curator, on remote EC2 instances. We should also collect disk statistics as well in a similar format, disk.json. Minimally the disk statistics should include the following:

• Disk partitions
• Disk configuration for each partition
  • File system type
  • Mount point name
• Disk usage for each partition
  • Total
  • Used
  • Free
• I/O counters for each partition
  • Read & Write operations
  • Read & Write bytes
  • Read & Write times (if available)