ipatests: Pretty print multihost config
    
    The printing of string representation of multihost config is useless.
    For example,
    ```
    <ipatests.pytest_ipa.integration.config.Config object at 0x7fe017d9dc70>
    ```
    
    The dictionary representation of such looks better:
    ```
    [ipatests.pytest_ipa.integration] {'ad_admin_name': 'Administrator',
     'ad_admin_password': 'Secret123',
     'admin_name': 'admin',
     'admin_password': 'Secret123',
     'dirman_dn': 'cn=Directory Manager',
     'dirman_password': 'Secret123',
     'dns_forwarder': '8.8.8.8',
     'domain_level': 1,
     'domains': [{'hosts': [{'external_hostname': 'master1.ipa.test',
                             'ip': '172.19.0.2',
                             'name': 'master1.ipa.test',
                             'role': 'master'},
                            {'external_hostname': 'replica1.ipa.test',
                             'ip': '172.19.0.3',
                             'name': 'replica1.ipa.test',
                             'role': 'replica'},
    ...
    ```
    
    Fixes: https://pagure.io/freeipa/issue/8265
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>