Disable coredumps by default

They consume a large amount of the CPU on the roboRIO.  This is grinding
it down to a halt and causing cascading failures right now.  It is a
flag now, so it is easy to change.

Change-Id: I1e09c2de731c12975de2de41fba74dd904a1f15c
diff --git a/aos/init.cc b/aos/init.cc
index 5d62868..c40f22c 100644
--- a/aos/init.cc
+++ b/aos/init.cc
@@ -24,6 +24,8 @@
 using FLAG__namespace_do_not_use_directly_use_DECLARE_double_instead::
     FLAGS_tcmalloc_release_rate;
 
+DEFINE_bool(coredump, false, "If true, write core dumps on failure.");
+
 namespace aos {
 namespace logging {
 namespace internal {
@@ -39,7 +41,9 @@
 // non-realtime initialization sequences. May be called twice.
 void InitStart() {
   ::aos::logging::Init();
-  WriteCoreDumps();
+  if (FLAGS_coredump) {
+    WriteCoreDumps();
+  }
   google::InstallFailureSignalHandler();
 }