Executor: Inconsistent behavior in pod reaper and executor backend

[life1347]

Currently, the environment metadata UID is cached in service function cache entry.
For a scenario like following

1. A user create an environment, which's UID is ooo-xxx
2. Create a function with that environment.
3. Delete the environment
4. Create a same name environment (but k8s assign different UID).

This scenario make behavior inconsistent in idle pod reaper and function pod scaling.

Use UID in pod reaper.

fission/executor/newdeploy/newdeploymgr.go

Lines 656 to 659 in 72faa92

	if _, ok := envList[fsvc.Environment.Metadata.UID]; !ok {
	log.Printf("Environment %v for function %v no longer exists",
	fsvc.Environment.Metadata.Name, fsvc.Name)
	}

Use env name to get env obj when scale pod deployment.

fission/executor/newdeploy/newdeploymgr.go

Lines 272 to 277 in 72faa92

	env, err := deploy.fissionClient.
	Environments(fn.Spec.Environment.Namespace).
	Get(fn.Spec.Environment.Name)
	if err != nil {
	return fsvc, err
	}