Fix tests

In core/test, it turns out that selenium is bringing in guava 15,
but the rest of Spark we use guava 14, which is evicted. Since
we made catalyst/test depend on core/test, and hive/test depends
on catalyst/test, hive tests are getting guava 15, which results
in java.lang.IllegalAccessError because of a dependency conflict.

This is resolved by excluding guava 15 from selenium in core/test.

core/pom.xml

@@ -338,6 +338,12 @@
     <dependency>
       <groupId>org.seleniumhq.selenium</groupId>
       <artifactId>selenium-java</artifactId>
+      <exclusions>
+        <exclusion>
+          <groupId>com.google.guava</groupId>
+          <artifactId>guava</artifactId>
+        </exclusion>
+      </exclusions>
       <scope>test</scope>
     </dependency>
     <!-- Added for selenium: -->