Fix issues with processes_sync

[sethboyles]

This PR fixes two issues with the process syncer:

Docker App LRPs are not deleted from Diego when diego_docker is disabled

This was a feature that was broken in this PR: #3503

Originally, disabling diego_docker was meant to stop all docker apps from being included in the process sync query, resulting them in being removed by the syncer.

This feature is documented here: https://docs.cloudfoundry.org/adminguide/docker.html#feature-flag

Deactivating the diego_docker feature flag stops all Docker-image-based apps in your deployment within a few convergence cycles, on the order of a one minute.

During #3503's performance improvement, this clause was moved out of the main query into the new subquery that happens when fetching processes for updates/desires. This meant the docker processes were never added to the array of LRPs to_delete, although they still were not considered for update/desire syncs.

ensure CNB apps are still synced if diego_docker is disabled

If diego_docker was disabled, then the query selected 'non_docker_type' processes. This queried for Buildpack processes, but excluded CNB processes.

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[sethboyles]

I'm not sure if a this subquery or two left joins like this would be more efficient:

left_join(BuildpackLifecycleDataModel.table_name, app_guid: :app_guid).
left_join(CNBLifecycleDataModel.table_name, app_guid: :app_guid).
)).

[philippthun]

Should we do the same for the feature flag docker_cnb? So that we end up with something like this?

app_guids = if !FeatureFlag.enabled?(:diego_docker) && !FeatureFlag.enabled?(:diego_cnb)
              BuildpackLifecycleDataModel.select(:app_guid)
            elsif !FeatureFlag.enabled?(:diego_docker)
              BuildpackLifecycleDataModel.select(:app_guid).union(CNBLifecycleDataModel.select(:app_guid))
            elsif !FeatureFlag.enabled?(:diego_cnb)
              BuildpackLifecycleDataModel.select(:app_guid).union(DockerLifecycleDataModel.select(:app_guid))
            end

processes = processes.where(Sequel.qualify(ProcessModel.table_name, :app_guid) => app_guids) unless app_guids.nil?

[sethboyles]

Should we do the same for the feature flag docker_cnb? So that we end up with something like this?

I considered that, but figured it would be best to keep this PR limited to restoring the intended behavior.

Another reason I didn't implement that is I wasn't sure of the intent behind the behavior and if we should treat CNBs the same--I believe some platform admins don't want to allow Docker apps for security reasons. Is that also true for CNBs? To me, it seemed like it was more likely we would eventually enable CNBs by default, but again I don't have a lot of context there.