SKS-2194: Fix labeling virtual machines

[haijianyang]

Issue SKS-2194

#162 给虚拟机增加虚拟机后，Tower 会自动给虚拟机添加系统标签导致 CAPE 不能给虚拟机添加预期的标签。

// 已经有了系统标签，导致没有进入 if 执行。
	if len(vm.Labels) == 0 {
		if ok, err := r.reconcileLabels(ctx, vm); !ok {
			return reconcile.Result{}, errors.Wrapf(err, "failed to reconcile labels")
		}
        }

Change

如果虚拟机打上了 managed 标签就认为所有的标签就有了，就可以跳过给虚拟机加标签的逻辑。

考虑每次 Reconcile 都要从 Tower 获取 managed 标签，且 managed 标签除非被人为删除，否则不会变动。为了减少 Tower 接口访问，managed 会缓存 30m。

Test

创建 1CP + 3Workers 集群，在 ElfCluster 指定 haijian.yang@d8dc20fc-e197-41da-83b6-c903c88663fd。

观察到虚拟机指定了 owner

虚拟机也打上了预期的标签

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (b2fb22f) 59.59% compared to head (3cdd60d) 59.92%.

Files	Patch %	Lines
controllers/elfmachine_controller.go	72.22%	3 Missing and 2 partials ⚠️
controllers/tower_cache.go	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
+ Coverage   59.59%   59.92%   +0.32%     
==========================================
  Files          20       20              
  Lines        3579     3603      +24     
==========================================
+ Hits         2133     2159      +26     
+ Misses       1297     1296       -1     
+ Partials      149      148       -1     

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[jessehu]

setLabelCache 改名为 setLabelInCache, 与 getLabelFromCache 名称对应。