test,android: set stdout and stderr line buffered

Sets stdout and stderr as line buffered in the android test
application. This reduces flakyness of tests caused by adb logcat
output adding additional newlines.

Author: jaimecbernardo

tools/mobile-test/android/testnode/app/src/main/cpp/native-lib.cpp

@@ -136,13 +136,15 @@ void* thread_stdout_func(void*) {
 }
 
 int start_redirecting_stdout_stderr() {
-    // Set stdout as unbuffered.
-    setvbuf(stdout, 0, _IONBF, 0);
+    // Set stdout as line buffered.
+    // Avoids additional line breaks caused by adb logcat splitting the output.
+    setvbuf(stdout, 0, _IOLBF, 0);
     pipe(pipe_stdout);
     dup2(pipe_stdout[1], STDOUT_FILENO);
 
-    // Set stderr as unbuffered.
-    setvbuf(stderr, 0, _IONBF, 0);
+    // Set stderr as line buffered.
+    // Avoids additional line breaks caused by adb logcat splitting the output.
+    setvbuf(stderr, 0, _IOLBF, 0);
     pipe(pipe_stderr);
     dup2(pipe_stderr[1], STDERR_FILENO);