Android tests call exit() when complete.

[ Merge of http://go/wvgerrit/119804 ]

The coverage framework used by Android requires the process to call
exit() for coverage information to be dumped after the tests.

Android unit tests have been adapted to use the a new main module.
The core test_main.cpp used by integration tests has been updated to
call exit().

Bug: 138941105
Test: Linux and Android unittests
Change-Id: Ifffc7b8290c50dffe527738a36547c1d2fb90bd3

libwvdrmengine/cdm/test/unit-test.mk

@@ -20,6 +20,7 @@ LOCAL_SRC_FILES := \
     ../core/test/url_request.cpp \
     ../../oemcrypto/test/oec_device_features.cpp \
     ../util/test/test_sleep.cpp \
+    ./cdm_test_main.cpp \
 
 LOCAL_C_INCLUDES := \
     vendor/widevine/libwvdrmengine/android/cdm/test \
@@ -44,7 +45,6 @@ LOCAL_STATIC_LIBRARIES := \
     libjsmn \
     libgmock \
     libgtest \
-    libgtest_main \
     libwvlevel3 \
 
 LOCAL_SHARED_LIBRARIES := \