Automatic merge from submit-queue (batch tested with PRs 62142, 62137, 62150, 62110). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Add subnet-id annotation for openstack cloud provider
Currently user only specify subnet-id in cloud.conf file.
If user want to specify other subnet for some special services,
the subnet-id annotation should be a good choice.
**Release note**:
```release-note
NONE
```
cc @sapham
827b3d77cd