Except properly if KSM not available

Signed-off-by: Jonathan Raffre <jonathan.raffre@nekolover.net>

In the current version, the Archipel Agent open forcefully /sys/kernel/mm/ksm/pages_sharing , even if it does not exists (this is the case on older kernels). 

This commit make this open safe and set memshared value to 0 if not found (which is the expected behavior, as there is no shared memory if KSM is not available).