a method to set virtualbox environment variables for docker-machine
            
        :return: True

def _set_virtualbox(self):
        
        '''
            a method to set virtualbox environment variables for docker-machine
            
        :return: True
        '''

        from os import environ
        if not environ.get('DOCKER_CERT_PATH'):
            import re
            sys_command = 'docker-machine env %s' % self.vbox
            cmd_output = self.command(sys_command)
            variable_list = ['DOCKER_TLS_VERIFY', 'DOCKER_HOST', 'DOCKER_CERT_PATH', 'DOCKER_MACHINE_NAME']
            for variable in variable_list:
                env_start = '%s="' % variable
                env_end = '"\\n'
                env_regex = '%s.*?%s' % (env_start, env_end)
                env_pattern = re.compile(env_regex)
                env_statement = env_pattern.findall(cmd_output)
                env_var = env_statement[0].replace(env_start, '').replace('"\n', '')
                environ[variable] = env_var

        return True