Add working internet precondition check

ConnectivityManagerTest expects a working internet before testing
but is not verified before each test. Add a working internet
check in setup to clearly test it.

Bug: 161370134
Test: atest CtsNetTestCasesLatestSdk:ConnectivityManagerTest
Change-Id: I47073ebff19fcf59d5d2ac86b43f8d54e621a55a
diff --git a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
index 0bba171..0790acb 100644
--- a/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
+++ b/tests/cts/net/src/android/net/cts/ConnectivityManagerTest.java
@@ -204,6 +204,8 @@
             } catch (Exception e) {}
         }
         mUiAutomation = mInstrumentation.getUiAutomation();
+
+        assertNotNull("CTS requires a working Internet connection", mCm.getActiveNetwork());
     }
 
     @After