snapshot: Fix leaked mounts and temp directories

Signed-off-by: Samuel Karp <skarp@amazon.com>

snapshot/common_test.go

@@ -0,0 +1,24 @@
+package snapshot
+
+import (
+	"os/exec"
+	"testing"
+
+	"github.com/docker/containerd"
+)
+
+func unmountAll(t *testing.T, mounts []containerd.Mount) {
+	for _, mount := range mounts {
+		unmount(t, mount.Target)
+	}
+}
+
+func unmount(t *testing.T, mountPoint string) {
+	t.Log("unmount", mountPoint)
+	umount := exec.Command("umount", mountPoint)
+	err := umount.Run()
+	if err != nil {
+
+		t.Error("Could not umount", mountPoint, err)
+	}
+}