free: handle memory statistics more than 4GB correctly

Integer.parseInt only can handle 32 bit integer, so it will throw
an exception if we have memory large than 4GB.

This patch use Long.parseLong() to replace Integer.parseInt().

Signed-off-by: Li Yu <raise.sail@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>