upgrades/validation: only run validation when services exist

upgrades/validation: only run validation when services exist

During upgrades, validation test if a service is running before the
upgrade process starts.
In some cases, servies doesn't exist yet so we don't want to run the
validation.

This patch makes sure we check if the service is actually present on the
system before validating it's running correctly.

Also it makes sure that services are enabled before trying to stop them.
It allows use-cases where we want to add new services during an upgrade.
Also install new packages of services added in Ocata, so we can validate
upgrades on scenarios jobs.

Change-Id: Ib48fb6b1557be43956557cbde4cbe26b53a50bd8