fix(Ads): Fix interstitials when not using multiple media elements (#8681)

Author: avelad

lib/ads/interstitial_ad_manager.js

@@ -224,6 +224,8 @@ shaka.ads.InterstitialAdManager = class {
         }
       }
     });
+
+    this.configure(this.basePlayer_.getConfiguration().ads);
   }
 
   /**
@@ -315,6 +317,7 @@ shaka.ads.InterstitialAdManager = class {
    */
   determineIfUsingBaseVideo_() {
     if (!this.adContainer_ || !this.config_ || this.playingAd_) {
+      this.usingBaseVideo_ = true;
       return;
     }
     let supportsMultipleMediaElements =
@@ -889,7 +892,8 @@ shaka.ads.InterstitialAdManager = class {
     this.determineIfUsingBaseVideo_();
     goog.asserts.assert(this.video_, 'Must have video');
 
-    if (!this.video_.parentElement && this.adContainer_) {
+    if (!this.usingBaseVideo_ && this.adContainer_ &&
+        !this.video_.parentElement) {
       this.adContainer_.appendChild(this.video_);
     }