'Enables OCSP Stapling
In OCSP, each client (e.g. browser) would have to query the
OCSP Responder to validate that the site certificate was not revoked.
Enabling OCSP Stapling, would allow the web-server to query the OCSP
Responder, and staple its response to the offered certificate during
TLS. i.e. clients would not have to query the OCSP responder.
OCSP Stapling enablement on Apache implicitly depends on
SSLCertificateChainFile being set by other code.
.. note:: This function saves the configuration
:param ssl_vhost: Destination of traffic, an ssl enabled vhost
:type ssl_vhost: :class:`~letsencrypt_apache.obj.VirtualHost`
:param unused_options: Not currently used
:type unused_options: Not Available
:returns: Success, general_vhost (HTTP vhost)
:rtype: (bool, :class:`~letsencrypt_apache.obj.VirtualHost`)'

def _enable_ocsp_stapling(self, ssl_vhost, unused_options):

    min_apache_ver = (2, 3, 3)
    if (self.get_version() < min_apache_ver):
        raise errors.PluginError('Unable    to    set    OCSP    directives.\nApache    version    is    below    2.3.3.')
    if ('socache_shmcb_module' not in self.parser.modules):
        self.enable_mod('socache_shmcb')
    use_stapling_aug_path = self.parser.find_dir('SSLUseStapling', 'on', start=ssl_vhost.path)
    if (not use_stapling_aug_path):
        self.parser.add_dir(ssl_vhost.path, 'SSLUseStapling', 'on')
    ssl_vhost_aug_path = self._escape(parser.get_aug_path(ssl_vhost.filep))
    stapling_cache_aug_path = self.parser.find_dir('SSLStaplingCache', None, ssl_vhost_aug_path)
    if stapling_cache_aug_path:
        self.aug.remove(re.sub('/\\w*$', '', stapling_cache_aug_path[0]))
    self.parser.add_dir_to_ifmodssl(ssl_vhost_aug_path, 'SSLStaplingCache', ['shmcb:/var/run/apache2/stapling_cache(128000)'])
    msg = ('OCSP    Stapling    was    enabled    on    SSL    Vhost:    %s.\n' % ssl_vhost.filep)
    self.save_notes += msg
    self.save()
    logger.info(msg)
