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: Ic01517a153406c8bafc672c20b0bf8686763a2f5
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>