Specify okhttp as a test dependency in apachehc

This is not transitively included somehow.

Author: gaul

drivers/apachehc/pom.xml

@@ -54,6 +54,11 @@
       <artifactId>jetty-security</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>com.squareup.okhttp3</groupId>
+      <artifactId>mockwebserver</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
 </project>