Fix usages of mountinfo.PrefixFilter

It says: The prefix path **must be absolute, have all symlinks resolved, and cleaned**. But those requirements are violated in lots of places.

What happens when it is given a non-canonicalized path is that `mountinfo.GetMounts` will not find mounts.

The trivial case is:
```
$ mkdir a && ln -s a b && mkdir b/c b/d && mount --bind b/c b/d && cat /proc/mounts | grep -- '[ab]/d'
/dev/sdd3 /home/user/a/d ext4 rw,noatime,discard 0 0
```
We asked to bind-mount b/c to b/d, but ended up with mount in a/d.
So, mount table always contains canonicalized mount points, and it is an error to look for non-canonicalized paths in it.

Signed-off-by: Marat Radchenko <marat@slonopotamus.org>

mount/lookup_unix.go

@@ -20,18 +20,15 @@ package mount
 
 import (
 	"fmt"
-	"path/filepath"
 
 	"github.com/moby/sys/mountinfo"
 )
 
 // Lookup returns the mount info corresponds to the path.
 func Lookup(dir string) (Info, error) {
-	dir = filepath.Clean(dir)
-
-	resolvedDir, err := filepath.EvalSymlinks(dir)
+	resolvedDir, err := CanonicalizePath(dir)
 	if err != nil {
-		return Info{}, fmt.Errorf("failed to resolve symlink for %q: %w", dir, err)
+		return Info{}, err
 	}
 
 	m, err := mountinfo.GetMounts(mountinfo.ParentsFilter(resolvedDir))