add the ec2 plugin + deps

https://wiki.jenkins-ci.org/display/JENKINS/Amazon+EC2+Plugin

playbooks/roles/tools_jenkins/defaults/main.yml

@@ -46,3 +46,7 @@ jenkins_tools_plugins:
   - { name: "github-oauth", version: "0.24" }
   - { name: "gradle", version: "1.25" }
   - { name: "credentials-binding", version: "1.9" }
+  - { name: "ec2", version: "1.36" }
+  - { name: "node-iterator-api", version: "1.5" }
+  - { name: "aws-java-sdk", version: "1.11.37" }
+  - { name: "aws-credentials", version: "1.11" }