RFC: Refactor resourceFactory

[amorenoz]

The issue of possibly refactoring the resourceFactory has come up a couple of times.

Opening this issue do discuss it. Some discussion topics could be:

• Should the resourceFactory be a singleton? That seems to be the current intention but I frankly doubt that's the actual case looking at the code:
  

  sriov-network-device-plugin/pkg/factory/factory.go

  Lines 39 to 49 in 89b9bc9

  	func NewResourceFactory(prefix, suffix string, pluginWatch bool) types.ResourceFactory {
  	if instance == nil {
  	return &resourceFactory{
  	endPointPrefix: prefix,
  	endPointSuffix: suffix,
  	pluginWatch: pluginWatch,
  	}
  	}
  	return instance
  	}

If so, how should we deal with the configuration (parameters to NewResourceFactory?)

• If it is a singleton, should all the modules that need it hold a reference to it and pass it down to their dependent objects or call a global GetInstance() function that returns the global instance?