Re-added mount_*.go in docker package to not break tests/build

Upstream-commit: 8b61af189597579f1086a42fcdc824bfe737dce7
Component: engine

components/engine/mount_darwin.go

@@ -0,0 +1,7 @@
+package docker
+
+import "errors"
+
+func mount(source string, target string, fstype string, flags uintptr, data string) (err error) {
+	return errors.New("mount is not implemented on darwin")
+}

components/engine/mount_linux.go

@@ -0,0 +1,8 @@
+package docker
+
+import "syscall"
+
+
+func mount(source string, target string, fstype string, flags uintptr, data string) (err error) {
+	return syscall.Mount(source, target, fstype, flags, data)
+}