lxc: Workaround against lxc changing logfile permissions

Running lxc-start changes the permissions of stdout/stderr to 700.

The previous workaround of changing the permissions back after lxc-status
only worked because of the lxc-status loop in container_manager.start

Make it more generic by applying it to every caller of helpers.lxc.start

See: https://github.com/lxc/lxc/blob/6564e6ccb22e6e3c6cf36e6ae3cb5d5f73122486/src/lxc/utils.c#L1859