libnativetesthelper_jni: print out all failures

Adding this test (for instance):
TEST_F(NdkBinderTest_AIBinder, FailTwice) {
  EXPECT_FALSE(true) << "first";
  EXPECT_FALSE(true) << "second";
}

Original error:

STACKTRACE:
java.lang.AssertionError: cts/tests/tests/binder_ndk/libbinder_ndk_test/test_ibinder.cpp:27
Value of: true
  Actual: true
Expected: false
second
    <stack>

Error after this CL:

STACKTRACE:
java.lang.AssertionError:
cts/tests/tests/binder_ndk/libbinder_ndk_test/test_ibinder.cpp:26
Value of: true
  Actual: true
Expected: false
first

cts/tests/tests/binder_ndk/libbinder_ndk_test/test_ibinder.cpp:27
Value of: true
  Actual: true
Expected: false
second

    <stack>

Bug: N/A
Test: see above
Change-Id: I5dcb80c16b22047873b1f6039b058603ebb2181b