Replace concrete Bastion Executor with Agnostik.
So everyone can use whatever they want as guarantee.

Based on #113 - clarify that this is a don't

Lock primitives (spinlock, mutex, semaphore, rwlock) should all have their is_locked() function.

This could be used in debugging assertions to make sure some golden rules are respected all along the kernel (lots of functions are assuming that some datas are already locked etc.).

Biggest beneficiaries are the vaspace_* functions. They assumes current thread and current virtual add