samples: tests refactored (GoogleCloudPlatform#3958)

Author: munkhuushmgl

video/beta/src/test/java/com/example/video/DetectFacesGcsIT.java

@@ -45,6 +45,6 @@ public void tearDown() {
   public void testDetectFacesGcs() throws Exception {
     DetectFacesGcs.detectFacesGcs("gs://cloud-samples-data/video/googlework_short.mp4");
     String got = bout.toString();
-    assertThat(got).contains("Attribute");
+    assertThat(got).contains("Face detected:");
   }
 }

video/beta/src/test/java/com/example/video/DetectFacesIT.java

@@ -46,6 +46,6 @@ public void tearDown() {
   public void testDetectFaces() throws Exception {
     DetectFaces.detectFaces("resources/googlework_short.mp4");
     String got = bout.toString();
-    assertThat(got).contains("Attribute");
+    assertThat(got).contains("Face detected:");
   }
 }