WifiManagerTest#testWifiWatchdog: Disambiguate failures

There is nothing in the WifiWatchdog test that supports the
assumption that the device under test is pre-configured with a
working WiFi network configuration.  This CL makes it possible
from the test stack trace whether the test failed at the
beginning or during the reconnections.

Bug: 27638295
Change-Id: Iff1bd398c74076fb1a969741818562ea582e868e

tests/cts/net/src/android/net/wifi/cts/WifiManagerTest.java

@@ -484,6 +484,9 @@ public class WifiManagerTest extends AndroidTestCase {
         }
         assertTrue(mWifiManager.isWifiEnabled());
 
+        // This will generate a distinct stack trace if the initial connection fails.
+        connectWifi();
+
         int i = 0;
         for (; i < 15; i++) {
             // Wait for a WiFi connection