Hi, LAVA Team!

I'm trying to add my new device. 
It must be flashed  by fastboot.
To turn device into fastboot mode, I need to write "reboot bootloader" via serial connection.
I have tried 
set soft_reboot_command = ['reboot bootloader']
and received error message
lava-lxc protocol: FAILED executing 'lxc-attach -n lxc-hikey-test-4 -- adb reboot bootloader'

Ilya