Rework function getContainers
Rework function getContainers

- Use canonical way to check if a map contains a key.
- Use "ci" to keep consistence since it is for "containerInfo".

Signed-off-by: Hu Keping <ce660952c949ad2751377b45317337be332e80ac@huawei.com>

crosbymichael/containerd,dmcgowan/containerd,mikebrow/containerd,hqhq/containerd,kunalkushwaha/containerd,crosbymichael/containerd,miaoyq/containerd,docker/containerd,miaoyq/containerd,kunalkushwaha/containerd,containerd/containerd,AkihiroSuda/containerd,xiekeyang/containerd,thaJeztah/containerd,containerd/containerd,dmcgowan/containerd,estesp/containerd,chanezon/containerd,vdemeester/containerd,amitkris/containerd,lichao-mobanche/containerd,thaJeztah/containerd,estesp/containerd,rajasec/containerd,yuexiao-wang/containerd,mikebrow/containerd,Wolphin-project/containerd,vdemeester/containerd,amitkris/containerd