Currently, shill does not pass any environment variables to l2tpipsec_vpn, except for 2 special ones: SHILL_TASK_SERVICE and SHILL_TASK_PATH, whose values are initialized by calls to RPCTaskAdaptorInterface::GetRpcConnectionIdentifier and RPCTaskAdaptorInterface::GetRpcIdentifier. We want to spawn l2tpipsec_vpn in minijail, but currently minijail doesn't support setting environment variables for spawned processes.

Need to add this functionality to minijail or find some workaround.

Code: L2TPIPSecDriver::SpawnL2TPIPSecVPN() --> ExternalTask::Start() --> RPCTask::GetEnvironment() --> RPCTaskAdaptorInterface::**()