Run valgrind on Lind

[rennergade]

We'd like to run vagrind on Lind to check for any memory leaks. Let's try to do this.

One issue is that our fork memory copy relies on mremap() which isn't allowed with valgrind. We can create and option to fallback to a straight memcpy the memory regions between cages on fork instead of the current setup and just enable that version when running valgrind.

[rennergade]

This is probably a good issue for @Yaxuan-w to work on once she gets the initial SGX traces, since it would also make fork "no kernel"