Enabling/disabling HPA/VPA should be done over Web UI

[juliababkina]

Now we can manage how many plugins to connect to Skenario via parameters in command line when we run Skenario (see Makefile).

We can run Skenario with only HPA - ./build/sim ./build/plugin-k8s
We can run Skenario with only VPA - ./build/sim ./build/plugin-k8s-vpa
We can run Skenario with both HPA and VPA - ./build/sim ./build/plugin-k8s ./build/plugin-k8s-vpa

When we run Skenario and feed plugins, Dispatcher starts these plugins as a separate process via Hashicorp https://github.com/pivotal/skenario/blob/master/plugin/pkg/skplug/dispatcher/dispatcher.go#L80.
Then Dispatcher registers plugin's capabilities https://github.com/pivotal/skenario/blob/master/plugin/pkg/skplug/dispatcher/dispatcher.go#L105

We want to manage this process - how many autoscalers we want to work with - via web ui. The checkboxes for both "HPA" and "VPA" are already added to the web ui. But we end up with an error:

• We run Skenario with both plugins
• Dispatcher registers their capabilities
• We uncheck one autoscaler
• Press "Execute Simulation"
• Skenario passes to Dispatcher stats
• Dispatcher knows two plugins with capability "stat" and send stats both of them.
• However, we created partition only for one plugin according to web ui.
• Here we get an error inside a plugin that partition doesn't exist. Which makes sense, because we said dispatcher that we are interesting only in one autoscaler and we need to create a partition only for it.

This logic should be fixed. Enabling/disabling HPA/VPA should be done over Web UI.