Use disk encryption for the root block device

[itsdalmo]

There is really no reason not to enable disk encryption, soencrypted = true needs to be set on the root_block_configuration as shown here:
https://www.terraform.io/docs/providers/aws/r/launch_configuration.html#root_block_device

Or if we switch to launch_template (#11) we can use this:
https://www.terraform.io/docs/providers/aws/r/launch_template.html#encrypted

[itsdalmo]

This will be a breaking change, so best done as part of #11 when terraform 0.12 is out.

[itsdalmo]

It does not seem like encryption can be enabled for the root device using launch_configuration, so we'll have to wait until we can swap to launch_template 🤔

[itsdalmo]

For the root block device to be enabled, encryption has to be enabled when creating the AMI.