test/py: Handle expected reset by command

Add wait_for_reboot optional argument to ConsoleBase::run_command()
so that it can handle an expected reset by command execution.

This is useful if a command will reset the sandbox while testing
such commands, e.g. run_command("reset", wait_for_reboot = True)

Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>