added a "test mode" for aos::Die and used it

ipc_stress_test was getting slowed down by disk I/O because of the
aos_fatal_error files getting written to /tmp and the stdout messages
that gtest doesn't capture were annoying, so I added a setting for
aos::Die to not do those things and used it in the ipc_stress_test
tests.
diff --git a/aos/common/die.cc b/aos/common/die.cc
index 467b81d..0ea7007 100644
--- a/aos/common/die.cc
+++ b/aos/common/die.cc
@@ -6,13 +6,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 #include <string.h>
-#ifdef __VXWORKS__
-#include <taskLib.h>
-// Have to re-declare it with __attribute__((noreturn)).
-extern "C" void abort() __attribute__((noreturn));
-#include <usrLib.h>
-#include <dbgLib.h>
-#endif
+#include <signal.h>
 
 #include <string>
 
@@ -28,6 +22,7 @@
 }
 
 namespace {
+
 // Calculates the filename to dump the message into.
 const std::string GetFilename() {
 #ifdef __VXWORKS__
@@ -50,6 +45,9 @@
   }
 #endif
 }
+
+bool test_mode = false;
+
 }  // namespace
 
 void VDie(const char *format, va_list args_in) {
@@ -60,31 +58,28 @@
   fputs("aos fatal: ERROR!! details following\n", stderr);
   va_copy(args1, args_in);
   vfprintf(stderr, format, args1);
-  fputs("aos fatal: ERROR!! see stderr for details\n", stdout);
+  if (!test_mode) {
+    fputs("aos fatal: ERROR!! see stderr for details\n", stdout);
 
-  const std::string filename = GetFilename();
-  if (!filename.empty()) {
-    FILE *error_file = fopen(filename.c_str(), "w");
-    if (error_file != NULL) {
-      va_copy(args2, args_in);
-      vfprintf(error_file, format, args2);
-      fclose(error_file);
-    } else {
-      fprintf(stderr, "aos fatal: fopen('%s', \"w\") failed with %d (%s)\n",
-              filename.c_str(), errno, strerror(errno));
+    const std::string filename = GetFilename();
+    if (!filename.empty()) {
+      FILE *error_file = fopen(filename.c_str(), "w");
+      if (error_file != NULL) {
+        va_copy(args2, args_in);
+        vfprintf(error_file, format, args2);
+        fclose(error_file);
+      } else {
+        fprintf(stderr, "aos fatal: fopen('%s', \"w\") failed with %d (%s)\n",
+                filename.c_str(), errno, strerror(errno));
+      }
     }
   }
 
-#ifdef __VXWORKS__
-  printf("I am 0x%x suspending for debugging purposes.\n", taskIdSelf());
-  printf("\t`tt 0x%x` will give you a stack trace.\n", taskIdSelf());
-  fputs("\t`lkAddr` will reverse lookup a symbol for you.\n", stdout);
-  fputs("\t`dbgHelp` and `help` have some useful commands in them.\n", stdout);
-  taskSuspend(0);
-  printf("You weren't supposed to resume 0x%x!!. Going to really die now.\n",
-         taskIdSelf());
-#endif
   abort();
 }
 
+void SetDieTestMode(bool new_test_mode) {
+  test_mode = new_test_mode;
+}
+
 }  // namespace aos