The AWSCredentialImpl API has changed in v1.17+:

https://github.com/jenkinsci/aws-credentials-plugin/commit/d12ab1def72f1577abf282a5d223aaa17f22c68e#diff-c0710975ba9b6383fc743f063dfb420dR71

This will result in the following code simply breaking for lack of constructor signature:

https://github.com/jenkinsci/ec2-plugin/blob/master/src/main/java/hudson/plugins/ec2/EC2Cloud.java#L231