Initialize MockWebServer in setUp() not construction time

Should be a no-op but makes test suite creation cheaper.

Bug: 29820565
Change-Id: Ieee5568a6f477d591436275be4d4e7e3d5dbd322

tests/cts/net/src/android/net/http/cts/HttpResponseCacheTest.java

@@ -38,10 +38,11 @@ import java.util.UUID;
 public final class HttpResponseCacheTest extends TestCase {
 
     private File cacheDir;
-    private MockWebServer server = new MockWebServer();
+    private MockWebServer server;
 
     @Override public void setUp() throws Exception {
         super.setUp();
+        server = new MockWebServer();
         String tmp = System.getProperty("java.io.tmpdir");
         cacheDir = new File(tmp, "HttpCache-" + UUID.randomUUID());
         cacheDir.mkdirs();