fix: Apiary Host returns user set host if set (#2455)

Bug: googleapis/java-bigquery#3125 (Removing
`Fixes:` as I don't want to close the ticket until BigQuery is able to
pull in a new version of shared-deps).

Following guidance in doc for Apiary (ping me internally for link).

If the user configures the host to be the `DEFAULT_HOST` (a non-valid
endpoint for any service using java-core), then it should construct a
valid service endpoint back using the universe domain.

Author: lqiu96

java-core/google-cloud-core/src/main/java/com/google/cloud/ServiceOptions.java

@@ -851,17 +851,24 @@ public String getResolvedHost(String serviceName) {
   }
 
   /**
-   * Temporarily used for BigQuery and Storage Apiary Wrapped Libraries. To be removed in the future
-   * when Apiary clients can resolve their endpoints. Returns the host to be used as the rootUrl.
+   * Returns a host value to be used for BigQuery and Storage Apiary Wrapped Libraries. To be
+   * removed in the future when Apiary clients can resolve their endpoints. Returns the host to be
+   * used as the rootUrl.
    *
    * <p>The resolved host will be in `https://{serviceName}.{resolvedUniverseDomain}/` format. The
    * resolvedUniverseDomain will be set to `googleapis.com` if universeDomain is null.
    *
+   * <p>The host value is set to DEFAULT_HOST if the user didn't configure a host. Returns the host
+   * value the user set, otherwise constructs the host for the user.
+   *
    * @see <a
    *     href="https://github.com/googleapis/google-api-java-client/blob/76765d5f9689be9d266a7d62fa6ffb4cabf701f5/google-api-client/src/main/java/com/google/api/client/googleapis/services/AbstractGoogleClient.java#L49">rootUrl</a>
    */
   @InternalApi
   public String getResolvedApiaryHost(String serviceName) {
+    if (!DEFAULT_HOST.equals(host)) {
+      return host;
+    }
     String resolvedUniverseDomain =
         universeDomain != null ? universeDomain : Credentials.GOOGLE_DEFAULT_UNIVERSE;
     return "https://" + serviceName + "." + resolvedUniverseDomain + "/";

java-core/google-cloud-core/src/test/java/com/google/cloud/ServiceOptionsTest.java

@@ -566,10 +566,10 @@ public void testGetResolvedApiaryHost_customUniverseDomain_customHost() {
     TestServiceOptions options =
         TestServiceOptions.newBuilder()
             .setUniverseDomain("test.com")
-            .setHost("https://service.random.com")
+            .setHost("https://service.random.com/")
             .setProjectId("project-id")
             .build();
-    assertThat(options.getResolvedApiaryHost("service")).isEqualTo("https://service.test.com/");
+    assertThat(options.getResolvedApiaryHost("service")).isEqualTo("https://service.random.com/");
   }
 
   // No User Configuration = GDU, Default Credentials = GDU