Fix Ubuntu 16.04 incompatibility with ssh-keyscan
Fix Ubuntu 16.04 incompatibility with ssh-keyscan

On error it returns 0 with stdout empty.  On Ubuntu 14.04,
it returned 255 exit status.

Fix is to ensure that stdout is not empty.

Change-Id: Id01717e420128f191541c825a0b97144780514d0

open-power-ref-design-toolkit/os-services,open-power-ref-design-toolkit/os-services,open-power-ref-design/os-services,open-power-ref-design/os-services,open-power-ref-design-toolkit/os-services