Ensure all test targets are built on Android.

When GYP runs for OS=android it doesn't generate the
video_engine_core_unittests_apk_target target which is needed to
get the APK built.
The same problem applies to webrtc/test/webrtc_test_common.gyp,
but that unittest is not added on any bot anyway, so that's future work.

TESTED=Ran webrtc/build/gyp_webrtc for Linux and Android locally.
Before this patch, the video_engine_core_unittests was not built
as part of the 'All' target. With this patch, it is now built.

R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1348093002 .

Cr-Commit-Position: refs/heads/master@{#9952}

webrtc/webrtc.gyp

@@ -68,8 +68,8 @@
             'system_wrappers/system_wrappers_tests.gyp:*',
             'test/metrics.gyp:*',
             'test/test.gyp:*',
-            'test/webrtc_test_common.gyp:webrtc_test_common_unittests',
-            'video_engine/video_engine_core_unittests.gyp:video_engine_core_unittests',
+            'test/webrtc_test_common.gyp:*',
+            'video_engine/video_engine_core_unittests.gyp:*',
             'webrtc_tests',
           ],
         }],