Add c3 instance types to Spark EC2

The number of disks for the c3 instance types taken from here: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html#StorageOnInstanceTypes

Author: Christian Lundgren <christian.lundgren@gameanalytics.com>

Closes #595 from chrisavl/branch-0.9 and squashes the following commits:

c8af5f9 [Christian Lundgren] Add c3 instance types to Spark EC2