vfs-cache: add a possibility to cache FsStat results

Acked-by: Dmitry Litvintsev
Target: master, 0.9
(cherry picked from commit 05f737ab6242f1086f39533e7e3f6770fc5e00bc)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>