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Add description of pvc condition for kubectl describe command
**What this PR does / why we need it**:
As the title says, add description of `PersistentVolumeClaim.Status.Conditions` for `kubectl describe pvc` command, the output will look like this:
```
Conditions:
Type Status LastProbeTime LastTransitionTime Reason Message
---- ------ ----------------- ------------------ ------ -------
Resizing True Mon, 01 Jan 0001 00:00:00 +0000 Sat, 10 Feb 2018 19:20:56 +0800
```
**Release note**:
```release-note
NONE
```
/sig storage
/kind enhancement
707b7fd179