This change cleans up the pod manager extensively so that
* Mirror pods are actually stored in the pod manager.
* Both (non-mirror) pods and mirror pods are indexed by UID and full name for
easy lookup and mapping. This is required for the next change to send
full pod along with the pod status update.
This change also renames mirrorManager as mirrorClient since it is merely a
client to contact the API server and create/delete mirror pods.
This change moves pod array and mirrorPods into podManager, along with all
methods accessing these internal pod storages. This is the first step of the
refactoring, and no function change is involved.
