Update CFN to allow starting of i2.2xlarge ES nodes
Add new EC2 I2 instance types
Fix/Add AMI mapping depending on instance virtualization type
Merge pull request #358 from cityindex/cfn-changes

Update CFN to allow starting of i2.2xlarge ES nodes
Merge remote-tracking branch 'origin/master' into issue-320
allow configuring daytime/fulltime instance types separately