use static keypair name

molecule/ec2-centos-7/create.yml

@@ -25,7 +25,7 @@
         to_port: 0
         cidr_ip: '0.0.0.0/0'
 
-    keypair_name: "molecule_key_{{ molecule_yml.platforms.name }}"
+    keypair_name: molecule_key_docker_engine
     keypair_path: "{{ lookup('env', 'MOLECULE_EPHEMERAL_DIRECTORY') }}/ssh_key"
   tasks:
     - name: Create security group