Raise exception when getting timeout for running cmd to detect OS

[lubaihua33]

For some images, like sciencelogicinc1622565452194, middleware publisher's images, running some basic commands will be time out. This is due to the image not allow to run commands or in bad state.

In _get_detect_string, there are more than 10 commands to detect the OS. If every command gets time out (10 min), the case might last longer than 1 hour.

The case should be go to the end immediately if the system can't run any commands.

In this PR, add timeout=30 for every command in _get_detect_string, and raise an exception when gets timeout to avoid more timeout commands.