ACME modules refactor (#187)

* Move acme.py to acme/__init__.py to prepare splitup.

* Began moving generic code out.

* Creating backends.

* Update unit tests.

* Move remaining new code out.

* Use new interface.

* Rewrite module init code.

* Add changelog.

* Add BackendException for crypto backend errors.

* Improve / uniformize ACME error reporting.

* Create ACMELegacyAccount for backwards compatibility.

* Split up ACMEAccount into ACMEClient and ACMEAccount.

* Move get_keyauthorization into module_utils.acme.challenges.

* Improve error handling.

* Move challenge and authorization handling code into module_utils.

* Add split_identifier helper.

* Move order code into module_utils.

* Move ACME v2 certificate handling code to module_utils.

* Fix/move ACME v1 certificate retrieval to module_utils as well.

* Refactor alternate chain handling code by splitting it up into simpler functions.

* Make chain matcher creation part of backend.

tests/unit/plugins/module_utils/acme/test_utils.py

@@ -0,0 +1,35 @@
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+import pytest
+
+
+from ansible_collections.community.crypto.plugins.module_utils.acme.utils import (
+    nopad_b64,
+    pem_to_der,
+)
+
+from .backend_data import (
+    TEST_PEM_DERS,
+)
+
+
+NOPAD_B64 = [
+    ("", ""),
+    ("\n", "Cg"),
+    ("123", "MTIz"),
+    ("Lorem?ipsum", "TG9yZW0_aXBzdW0"),
+]
+
+
+@pytest.mark.parametrize("value, result", NOPAD_B64)
+def test_nopad_b64(value, result):
+    assert nopad_b64(value.encode('utf-8')) == result
+
+
+@pytest.mark.parametrize("pem, der", TEST_PEM_DERS)
+def test_pem_to_der(pem, der, tmpdir):
+    fn = tmpdir / 'test.pem'
+    fn.write(pem)
+    assert pem_to_der(str(fn)) == der