New certificate management module.

There is a new certificate management module placed in the plugins
folder:

    plugins/modules/ipacert.py

The certificate module allows to request, revoke, release and retrieve
certificates for users, hosts and services.

Here is the documentation for the module:

    README-cert.md

New example playbooks have been added:

    playbooks/cert/cert-hold.yml
    playbooks/cert/cert-release.yml
    playbooks/cert/cert-request-host.yml
    playbooks/cert/cert-request-service.yml
    playbooks/cert/cert-request-user.yml
    playbooks/cert/cert-retrieve.yml
    playbooks/cert/cert-revoke.yml

New tests for the module can be found at:

    tests/cert/test_cert_client_context.yml
    tests/cert/test_cert_host.yml
    tests/cert/test_cert_service.yml
    tests/cert/test_cert_user.yml

The module has been co-authored by Sam Morris (@yrro) and Rafael
Guterres Jeffman (@rjeffman).

playbooks/cert/cert-request-host.yml

@@ -0,0 +1,26 @@
+---
+- name: Certificate manage example
+  hosts: ipaserver
+  become: false
+  gather_facts: false
+  module_defaults:
+    ipacert:
+      ipaadmin_password: SomeADMINpassword
+      ipaapi_context: client
+
+  tasks:
+  - name: Request a certificate for a host
+    ipacert:
+      csr: |
+        -----BEGIN CERTIFICATE REQUEST-----
+        MIIBWjCBxAIBADAbMRkwFwYDVQQDDBBob3N0LmV4YW1wbGUuY29tMIGfMA0GCSqG
+        SIb3DQEBAQUAA4GNADCBiQKBgQCzR3Vd4Cwl0uVgwB3+wxz+4JldFk3x526bPeuK
+        g8EEc+rEHILzJWeXC8ywCYPOgK9n7hrdMfVQiIx3yHYrY+0IYuLehWow4o1iJEf5
+        urPNAP9K9C4Y7MMXzzoQmoWR3IFQQpOYwvWOtiZfvrhmtflnYEGLE2tgz53gOQHD
+        NnbCCwIDAQABoAAwDQYJKoZIhvcNAQELBQADgYEAgF+6YC39WhnvmFgNz7pjAh5E
+        2ea3CgG+zrzAyiSBGG6WpXEjqMRnAQxciQNGxQacxjwWrscZidZzqg8URJPugewq
+        tslYB1+RkZn+9UWtfnWvz89+xnOgco7JlytnbH10Nfxt5fXXx13rY0tl54jBtk2W
+        422eYZ12wb4gjNcQy3A=
+        -----END CERTIFICATE REQUEST-----
+      principal: host/host.example.com
+      state: requested