Automatic merge from submit-queue (batch tested with PRs 58661, 58764, 58368, 58739, 58773). 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 cloud provider] Ensure hosts are updated in EnsureLoadBalancer()

**What this PR does / why we need it**:
From https://github.com/kubernetes/kubernetes/issues/56527, the `EnsureLoadBalancer()` implementation in GCE external LB doesn't always update the hosts (nodes). This PR makes it to do so.

Previously, the only situation where `ensureExternalLoadBalancer()` will not update hosts is when hosts are updated but there is no other changes that trigger target pool update (for which we delete&recreate target pool and hence updates the hosts). So the main change here is detecting that condition and call `updateTargetPool()`.

**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 #56527

**Special notes for your reviewer**:
Turned out it could be a small change, so I gave it a try.
/assign @nicksardo @bowei 

**Release note**:

```release-note
NONE
```