Remove PyOpenSSL backends (except for openssl_pkcs12) (#273)

* Remove Ubuntu 16.04 (Xenial Xerus) from CI.

* Removing PyOpenSSL backend from everywhere but openssl_pkcs12.

* Remove PyOpenSSL support from module_utils that's not needed for openssl_pkcs12.

* Add changelog fragment.

tests/integration/targets/openssl_csr_pipe/meta/main.yml

@@ -1,4 +1,3 @@
 dependencies:
   - setup_openssl
-  - setup_pyopenssl
   - setup_remote_tmp_dir

tests/integration/targets/openssl_csr_pipe/tasks/main.yml

@@ -14,24 +14,6 @@
     subject:
       commonName: www.ansible.com
 
-- block:
-  - name: Running tests with pyOpenSSL backend
-    include_tasks: impl.yml
-    vars:
-      select_crypto_backend: pyopenssl
-
-  when: pyopenssl_version.stdout is version('0.15', '>=')
-
-- name: Remove output directory
-  file:
-    path: "{{ remote_tmp_dir }}"
-    state: absent
-
-- name: Re-create output directory
-  file:
-    path: "{{ remote_tmp_dir }}"
-    state: directory
-
 - block:
   - name: Running tests with cryptography backend
     include_tasks: impl.yml