Change octavia private key ciphers to type 'auto'

Modern ansible only supports the 'cryptography' backend for the
openssl_privatekey module. In this case, the 'cipher' module
parameter must be set to 'auto'.

Change-Id: I2bfe5fa57c7deb201f56f82d5699c91fcccb766d

defaults/main.yml

@@ -435,8 +435,8 @@ octavia_cert_dir: "{{ lookup('env', 'HOME') }}/openstack-ansible/octavia"
 octavia_cert_dir_owner: "{{ lookup('env', 'USER') }}"
 
 octavia_cert_key_length_server: '4096' # key length
-octavia_cert_cipher_server: 'aes256'
-octavia_cert_cipher_client: 'aes256'
+octavia_cert_cipher_server: 'auto'
+octavia_cert_cipher_client: 'auto'
 octavia_cert_key_length_client: '4096' # key length
 octavia_cert_server_ca_subject: '/C=US/ST=Denial/L=Nowhere/O=Dis/CN=www.example.com' # change this to something more real
 octavia_cert_client_ca_subject: '/C=US/ST=Denial/L=Nowhere/O=Dis/CN=www.example.com' # change this to something more real