Raise exception in wget when timeout and increase timeout for wget in mshv stress test

[pupacha]

wget: raise exception if wget times out

When wget times out, the downloaded file will be in corrupted state.
Lisa should raise exception in this case, instead of returning the
corrupted downloaded path.


mshv: Increase timeout when downloading guest image

The ubuntu cloud image is usually of 2GB size and sometimes, due to
network delays, it might take more than the default 600s time to
download it. So, increase it to 1200.