Make GetFullyQualifiedHomeserverName easier to use in tests

Example:
```
alice.MustJoinRoom(t, bobRoomID, []string{
	shardDeployment2.GetFullyQualifiedHomeserverName(t, "hs1"),
})
```

Author: MadLittleMods

internal/docker/deployment.go

@@ -57,14 +57,14 @@ func (hsDep *HomeserverDeployment) SetEndpoints(baseURL string, fedBaseURL strin
 	}
 }
 
-func (d *Deployment) GetFullyQualifiedHomeserverName(hsName string) (string, error) {
+func (d *Deployment) GetFullyQualifiedHomeserverName(t ct.TestLike, hsName string) string {
 	_, ok := d.HS[hsName]
 	if !ok {
-		return "", fmt.Errorf("Deployment.GetFullyQualifiedHomeserverName - HS name '%s' not found", hsName)
+		ct.Fatalf(t, "Deployment.GetFullyQualifiedHomeserverName - HS name '%s' not found", hsName)
 	}
 	// We have network aliases for each Docker container that will resolve the `hsName` to
 	// the container.
-	return hsName, nil
+	return hsName
 }
 
 // DestroyAtCleanup destroys the entire deployment. It should be called at cleanup time for dirty

test_package.go

@@ -20,12 +20,13 @@ import (
 
 // Deployment provides a way for tests to interact with a set of homeservers.
 type Deployment interface {
-	// Returns the resolvable host name of a homeserver given its short alias (e.g.,
-	// "hs1", "hs2").
+	// Returns the resolvable server name (host) of a homeserver given its short alias
+	// (e.g., "hs1", "hs2").
 	//
 	// In the case of the standard Docker deployment, this will be the same `hs1`, `hs2`
-	// but may be different for other custom deployments.
-	GetFullyQualifiedHomeserverName(hsName string) (string, error)
+	// but may be different for other custom deployments (ex.
+	// `shardDeployment1.GetFullyQualifiedHomeserverName(t, "hs1")` -> `hs1.shard1:8081`).
+	GetFullyQualifiedHomeserverName(t ct.TestLike, hsName string) string
 	// UnauthenticatedClient returns a blank CSAPI client.
 	UnauthenticatedClient(t ct.TestLike, serverName string) *client.CSAPI
 	// Register a new user on the given server.