Move key_global into RemoteAllocator (#608)

There was a mis-compilation in a Verona configuration that lead to
two instances of key_global existing.  This change moves it inside
a struct that seems to fix the issue.

The rest of the changes are limiting the use of key_global as both
RemoteCache and RemoteAllocator must use the same configuration,
so there is no need to take the key_global as a parameter.

src/test/func/domestication/domestication.cc

@@ -138,7 +138,7 @@ int main()
 
   LocalEntropy entropy;
   entropy.init<DefaultPal>();
-  key_global = FreeListKey(entropy.get_free_list_key());
+  RemoteAllocator::key_global = FreeListKey(entropy.get_free_list_key());
 
   auto alloc1 = new Alloc();