Merge pull request #58561 from jesseshieh/patch-1

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Fix master regex when running multiple clusters

**What this PR does / why we need it**:
I'm running two Kubernetes clusters on GCE. One for production and one for staging. The instance prefix I use for production is `kubernetes` and for staging it's `staging-kubernetes`. This caused a problem when running `kube-up.sh` for production because when it tries to find all instances which match `kubernetes(-...)?` it finds both the production and staging instances. This probably results in multiple problems, but the most noticeable one for me was that `INITIAL_ETCD_CLUSTER` was incorrect and so etcd wouldn't start up correctly so the api server doesn't start up correctly so nothing else starts up. I tested this manually and it seems to work for me, but I didn't write an automated test.

**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 #

**Special notes for your reviewer**:

**Release note**:

```release-note
Fixes bug finding master replicas in GCE when running multiple Kubernetes clusters
```

cluster/gce/util.sh

@@ -1868,7 +1868,7 @@ function get-master-replicas-count() {
 # Prints regexp for full master machine name. In a cluster with replicated master,
 # VM names may either be MASTER_NAME or MASTER_NAME with a suffix for a replica.
 function get-replica-name-regexp() {
-  echo "${MASTER_NAME}(-...)?"
+  echo "^${MASTER_NAME}(-...)?"
 }
 
 # Sets REPLICA_NAME to a unique name for a master replica that will match