DEBUG/MINOR: memory: add a build option to disable memory pools sharing

Sometimes analysing a core file isn't easy due to shared memory pools.
Let's add a build option to disable this. It's not enabled by default,
it could be backported to older versions.
diff --git a/include/common/memory.h b/include/common/memory.h
index c76b4ca..af4e653 100644
--- a/include/common/memory.h
+++ b/include/common/memory.h
@@ -28,7 +28,11 @@
 #include <common/config.h>
 #include <common/mini-clist.h>
 
+#ifndef DEBUG_DONT_SHARE_POOLS
 #define MEM_F_SHARED	0x1
+#else
+#define MEM_F_SHARED	0
+#endif
 
 struct pool_head {
 	void **free_list;