core: host-deploy: Wrap validation of fingerprint using EngineSSHClient

By setting VDS object to EngineSSHClient, we initialize sshClient
parameters hostname, port and ssh username and can get the stored
fingerprint from the vds object for validation.

Change-Id: Ie0ce892c90844bc157e9b2feaba6aeca8acad78d
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>