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>

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

Supplementing the fix/commit 748315620bbbc472652e38df960d136beee4882e
While remote executing commands through ssh, wait for channel condition of EXIT_STATUS.

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