isolate and mark platform dependent code

now unit tests compile on OS X and (some of them) work

util/util_linux.go

@@ -0,0 +1,41 @@
+// +build linux
+
+package util
+
+import (
+	"os"
+	"syscall"
+
+	"github.com/docker/docker/pkg/mount"
+)
+
+func mountProc() error {
+	if _, err := os.Stat("/proc/self/mountinfo"); os.IsNotExist(err) {
+		if _, err := os.Stat("/proc"); os.IsNotExist(err) {
+			if err = os.Mkdir("/proc", 0755); err != nil {
+				return err
+			}
+		}
+
+		if err := syscall.Mount("none", "/proc", "proc", 0, ""); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func Mount(device, directory, fsType, options string) error {
+	if err := mountProc(); err != nil {
+		return nil
+	}
+
+	if _, err := os.Stat(directory); os.IsNotExist(err) {
+		err = os.MkdirAll(directory, 0755)
+		if err != nil {
+			return err
+		}
+	}
+
+	return mount.Mount(device, directory, fsType, options)
+}