cockpit-ovirt: admin and appliance passwords saved in plain text variable file during HE deployment

During HE deployment via cockpit-ovirt, cockpit-ovirt generates an ansible variable file `/var/lib/ovirt-hosted-engine-setup/cockpit/ansibleVarFileXXXXXX.var` which contains the admin and the appliance passwords as plain-text. At the of the deployment procedure, these files are deleted.