7.15.1 release

[elasticmachine]

7.15.1

• 7.15.1 as default version.

[Conky5]

Test failures, not sure if these are expected or not https://devops-ci.elastic.co/job/elastic+ansible-elasticsearch+pull-request-6x/58/

jenkins test this please

[Conky5]

No more ubuntu-1604 error, so I think everything except ubuntu-1404 that failed is potentially flaky can can be ignored https://devops-ci.elastic.co/job/elastic+ansible-elasticsearch+pull-request/289/

The ubuntu-1404 failures look to be do to certificates and are unrelated to this PR, so I am going to ignore them too https://devops-ci.elastic.co/job/elastic+ansible-elasticsearch+pull-request/289/OS=ubuntu-1404,TEST_TYPE=default,label=linux/consoleText

       TASK [elasticsearch : Debian - Add Elasticsearch repository key] ***************
       fatal: [localhost]: FAILED! => {"changed": false, "msg": "Failed to validate the SSL certificate for artifacts.elastic.co:443. Make sure your managed systems have a valid CA certificate installed. If the website serving the url uses SNI you need python >= 2.7.9 on your managed machine  (the python executable used (/usr/bin/python) is version: 2.7.6 (default, Nov 13 2018, 12:45:42) [GCC 4.8.4]) or you can install the `urllib3`, `pyOpenSSL`, `ndg-httpsclient`, and `pyasn1` python modules to perform SNI verification in python >= 2.6. You can use validate_certs=False if you do not need to confirm the servers identity but this is unsafe and not recommended. Paths checked for this platform: /etc/ssl/certs, /etc/pki/ca-trust/extracted/pem, /etc/pki/tls/certs, /usr/share/ca-certificates/cacert.org, /etc/ansible. The exception msg was: [Errno 1] _ssl.c:510: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed.", "status": -1, "url": "https://artifacts.elastic.co/GPG-KEY-elasticsearch"}