Embed pymysql within the collection and use default test container

This change eliminates the need to install the connector on each
controlled node, as `pymysql` version 1.1.1 is now included. As a
result, we can safely assume its availability, thus simplifying the
testing process.

Also, I managed to remove the need for pre-built test containers. We
now use the default test containers from ansible-test.

tests/integration/targets/test_mysql_variables/tasks/issue-28.yml

@@ -48,19 +48,8 @@
         login_port: '{{ mysql_primary_port }}'
         ca_cert: /tmp/cert.pem
       register: result
-      ignore_errors: yes
-
-    - assert:
-        that:
-          - result is failed
-      when:
-        - connector_name == 'pymysql'
-
-    - assert:
-        that:
-          - result is succeeded
-      when:
-        - connector_name != 'pymysql'
+      failed_when:
+        - result is success
 
     - name: attempt connection with newly created user ignoring hostname
       mysql_variables:
@@ -70,13 +59,7 @@
         login_host: '{{ mysql_host }}'
         login_port: '{{ mysql_primary_port }}'
         ca_cert: /tmp/cert.pem
-        check_hostname: no
-      register: result
-      ignore_errors: yes
-
-    - assert:
-        that:
-          - result is succeeded or 'pymysql >= 0.7.11 is required' in result.msg
+        check_hostname: false
 
     - name: Drop mysql user
       mysql_user: