Enable Webdriver test in Kokoro build

We changed to use Docker to provision Chrome browser and
ChromeDriverService, and the used Kokoro VM comes with
the docker CLI so we can enable the webdriver tests again
in kokoro build.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=237874165

gradle/core/build.gradle

@@ -647,11 +647,8 @@ test {
   exclude "**/*TestCase.*", "**/*TestSuite.*"
   exclude fragileTestPatterns
   exclude outcastTestPatterns
-  if (rootProject.hasProperty("excludeWebDriverTests")) {
-      exclude "**/webdriver/*"
-  } else {
-      dependsOn dockerRun
-  }
+
+  dependsOn dockerRun
 
   // Run every test class in its own process.
   // Uncomment to unblock build while troubleshooting inexplicable test errors.
@@ -667,10 +664,8 @@ test {
     new File(screenshotsDir).deleteDir()
   }
 }.dependsOn(fragileTest, outcastTest)
+test.finalizedBy(dockerStopAtEnd)
 
-if (!rootProject.hasProperty("excludeWebDriverTests")) {
-  test.finalizedBy(dockerStopAtEnd)
-}
 
 task nomulus(type: Jar) {
   manifest {