Encrypt httpd key stored on disk
    
    This commit adds configuration for HTTPD to encrypt/decrypt its
    key which we currently store in clear on the disc.
    
    A password-reading script is added for mod_ssl. This script is
    extensible for the future use of directory server with the
    expectation that key encryption/decription will be handled
    similarly by its configuration.
    
    https://pagure.io/freeipa/issue/7421
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>