Automatic merge from submit-queue. 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>.
[GCE Ingress e2e] Add test for pre-shared certificate
**What this PR does / why we need it**:
Add an e2e test for the pre-shared certificate feature (`ingress.gcp.kubernetes.io/pre-shared-cert`). Also made some changes to ingress_util.go mostly for certificate generation and polling on ingress.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #NONE
**Special notes for your reviewer**:
/assign @rramkumar1 @nicksardo
**Release note**:
```release-note
NONE
```
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