Call SetShmBase() in init_rs

The ShmEventLoop rust test was using /dev/shm/aos and breaking out of
the sandbox. Fix that.

Change-Id: I14db8b500a03a66fef41399c4cea334ff79b217f
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/ipc_lib/shm_base.cc b/aos/ipc_lib/shm_base.cc
new file mode 100644
index 0000000..22bf915
--- /dev/null
+++ b/aos/ipc_lib/shm_base.cc
@@ -0,0 +1,9 @@
+#include "aos/ipc_lib/shm_base.h"
+
+DEFINE_string(shm_base, "/dev/shm/aos",
+              "Directory to place queue backing mmaped files in.");
+namespace aos::testing {
+void SetShmBase(const std::string_view base) {
+  FLAGS_shm_base = std::string(base) + "/aos";
+}
+}  // namespace aos::testing