[KYUUBI #1611] Fix swagger-ui redirect wrong to other service address

<!--
Thanks for sending a pull request!

Here are some tips for you:
  1. If this is your first time, please read our contributor guidelines: https://kyuubi.readthedocs.io/en/latest/community/contributions.html
  2. If the PR is related to an issue in https://github.com/apache/incubator-kyuubi/issues, add '[KYUUBI #XXXX]' in your PR title, e.g., '[KYUUBI #XXXX] Your PR title ...'.
  3. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP][KYUUBI #XXXX] Your PR title ...'.
-->

### _Why are the changes needed?_
<!--
Please clarify why the changes are needed. For instance,
  1. If you add a feature, you can talk about the use case of it.
  2. If you fix a bug, you can clarify why it is a bug.
-->

close #1611

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [ ] [Run test](https://kyuubi.readthedocs.io/en/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #1615 from cfmcgrady/kyuubi-1611.

Closes #1611

f44bf3b [Fu Chen] fix swagger-ui

Authored-by: Fu Chen <cfmcgrady@gmail.com>
Signed-off-by: ulysses-you <ulyssesyou@apache.org>

Author: cfmcgrady

kyuubi-server/src/main/scala/org/apache/kyuubi/server/api/v1/ApiRootResource.scala

@@ -23,7 +23,7 @@ import javax.ws.rs.core.{MediaType, Response}
 
 import com.google.common.annotations.VisibleForTesting
 
-import org.apache.kyuubi.server.KyuubiServer
+import org.apache.kyuubi.server.{KyuubiRestFrontendService, KyuubiServer}
 import org.apache.kyuubi.server.api.ApiRequestContext
 
 @Path("/api/v1")
@@ -53,7 +53,11 @@ private[v1] class ApiRootResource extends ApiRequestContext {
   @Path("swagger-ui")
   @Produces(Array(MediaType.TEXT_HTML))
   def swaggerUi(): Response = {
-    val serverIP = KyuubiServer.kyuubiServer.frontendServices.head.connectionUrl
+    val restServiceOpt = KyuubiServer.kyuubiServer
+      .frontendServices
+      .collectFirst { case rest: KyuubiRestFrontendService => rest }
+    assert(restServiceOpt.isDefined)
+    val serverIP = restServiceOpt.map(_.connectionUrl).get
     val swaggerUi =
       s"http://$serverIP/swagger-ui-redirected/index.html?url=http://$serverIP/openapi.json"
     Response.temporaryRedirect(new URI(swaggerUi)).build()