CLOUDSTACK-4911 - [Mixed Hypervisor] VM Status is marked as alive when exit status of ping command is not available within command timeout

Currently during ssh execution of remote command, if no response is received within timeout, Cloudstack is returning success result.
This is resulting in false positives. Fix is to check if exit status of remote command is available or not. If not, return failure result.

Signed-off-by: Sateesh Chodapuneedi <sateesh@apache.org>