mount: replace mountinfo handling with moby/sys/mountinfo

Trying to reduce duplicated effort in maintaining a mountinfo
parser, this patch replaces the local implementation with the
implementation in github.com/moby/sys, which is actively maintained
and contains various optimizations.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/sys/mountinfo/mountinfo.go

@@ -0,0 +1,63 @@
+package mountinfo
+
+import (
+	"os"
+)
+
+// GetMounts retrieves a list of mounts for the current running process,
+// with an optional filter applied (use nil for no filter).
+func GetMounts(f FilterFunc) ([]*Info, error) {
+	return parseMountTable(f)
+}
+
+// Mounted determines if a specified path is a mount point.
+//
+// The argument must be an absolute path, with all symlinks resolved, and clean.
+// One way to ensure it is to process the path using filepath.Abs followed by
+// filepath.EvalSymlinks before calling this function.
+func Mounted(path string) (bool, error) {
+	// root is always mounted
+	if path == string(os.PathSeparator) {
+		return true, nil
+	}
+	return mounted(path)
+}
+
+// Info reveals information about a particular mounted filesystem. This
+// struct is populated from the content in the /proc/<pid>/mountinfo file.
+type Info struct {
+	// ID is a unique identifier of the mount (may be reused after umount).
+	ID int
+
+	// Parent indicates the ID of the mount parent (or of self for the top of the
+	// mount tree).
+	Parent int
+
+	// Major indicates one half of the device ID which identifies the device class.
+	Major int
+
+	// Minor indicates one half of the device ID which identifies a specific
+	// instance of device.
+	Minor int
+
+	// Root of the mount within the filesystem.
+	Root string
+
+	// Mountpoint indicates the mount point relative to the process's root.
+	Mountpoint string
+
+	// Options represents mount-specific options.
+	Options string
+
+	// Optional represents optional fields.
+	Optional string
+
+	// FSType indicates the type of filesystem, such as EXT3.
+	FSType string
+
+	// Source indicates filesystem specific information or "none".
+	Source string
+
+	// VFSOptions represents per super block options.
+	VFSOptions string
+}