'Add a health check to a target pool.
:param  targetpool: The targetpool to add health check to
:type   targetpool: ``str`` or :class:`GCETargetPool`
:param  healthcheck: The healthcheck to add
:type   healthcheck: ``str`` or :class:`GCEHealthCheck`
:return: True if successful
:rtype:  ``bool``'

def ex_targetpool_add_healthcheck(self, targetpool, healthcheck):

    if (not hasattr(targetpool, 'name')):
        targetpool = self.ex_get_targetpool(targetpool)
    if (not hasattr(healthcheck, 'name')):
        healthcheck = self.ex_get_healthcheck(healthcheck)
    targetpool_data = {'healthChecks': [{'healthCheck': healthcheck.extra['selfLink']}]}
    request = ('/regions/%s/targetPools/%s/addHealthCheck' % (targetpool.region.name, targetpool.name))
    self.connection.async_request(request, method='POST', data=targetpool_data)
    targetpool.healthchecks.append(healthcheck)
    return True
