irmap: Add option that forces fsnotify watches paths resolve

When migrating container with copying its FS, the inode numbers
and thus their handles wil change. This will make the restore of
inotify/fanotify fail, since they do it via fhandles.

We've already faced the problems with fsnotifies on NFS -- they
don't work there. To address this an irmap cache is created on
pre-dump, so to resolve the issue with changed inodes during
migration, we can force the irmap cache build.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>