vfs: introduce short cache of a parent inode on create

A typical open -> write -> close sequence translated into series of a
NFS operations OPEN -> LAYOUTGET -> WRITE -> CLOSE.
In case of dCache, LAYOUTGET triggers storageinfo read by.
As for newly created files, storageinfo are the same as for
parent directory, we need an cheap way to access parent
information. The introduced short cache time is good enough
for most workloads.

Target: master
Acked-By: Albert Rossi
vfs-cache: use  LoadingCache for caching

Target: master
Acked-By: Albert Rossi