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>.

Fix update-swagger-spec.sh to always cleanup etcd

**What this PR does / why we need it**:
This PR fixes `hack/update-swagger-spec.sh` so it always cleanup etcd and to noe leave orphaned process after its execution. This process also doesn't allow to run the script again as it detects existing etcd and won't start.

I also made a minor improvement by adding guard against an empty arguments.

**Release note**:
```release-note
NONE
```

CC @simo5