Recognize `encrypted` keyword for ec2 volumes
- added for both `create_volume()` and `create_attach_volumes()`
- requires EC2 API version `2014-10-01`
- announcment:
  - https://aws.amazon.com/about-aws/whats-new/2014/05/21/Amazon-EBS-encryption-now-available/
Merge pull request #18946 from walgitrus/ec2-encrypted-ebs

Recognize `encrypted` keyword for ec2 volumes