Add phase 1 of validation tightening.

https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/177-volume-snapshot/tighten-validation-webhook-crd.md

1. Ratcheting validation webhook server image
2. Controller labels invalid objects
3. Unit tests for webhook
4. Deployment README and example deployment method with certs
5. Update top-level README

Racheting validation:
1. webhook is strict on create
2. webhook is strict on updates where the existing object passes strict validation
3. webhook is relaxed on updates where the existing object fails strict validation (allows finalizer removal, status update, deletion, etc)

Additionally the validating wehook server will perform immutability
checks on scenario 2 above.

vendor/github.com/inconshreveable/mousetrap/trap_windows.go

@@ -0,0 +1,98 @@
+// +build windows
+// +build !go1.4
+
+package mousetrap
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	// defined by the Win32 API
+	th32cs_snapprocess uintptr = 0x2
+)
+
+var (
+	kernel                   = syscall.MustLoadDLL("kernel32.dll")
+	CreateToolhelp32Snapshot = kernel.MustFindProc("CreateToolhelp32Snapshot")
+	Process32First           = kernel.MustFindProc("Process32FirstW")
+	Process32Next            = kernel.MustFindProc("Process32NextW")
+)
+
+// ProcessEntry32 structure defined by the Win32 API
+type processEntry32 struct {
+	dwSize              uint32
+	cntUsage            uint32
+	th32ProcessID       uint32
+	th32DefaultHeapID   int
+	th32ModuleID        uint32
+	cntThreads          uint32
+	th32ParentProcessID uint32
+	pcPriClassBase      int32
+	dwFlags             uint32
+	szExeFile           [syscall.MAX_PATH]uint16
+}
+
+func getProcessEntry(pid int) (pe *processEntry32, err error) {
+	snapshot, _, e1 := CreateToolhelp32Snapshot.Call(th32cs_snapprocess, uintptr(0))
+	if snapshot == uintptr(syscall.InvalidHandle) {
+		err = fmt.Errorf("CreateToolhelp32Snapshot: %v", e1)
+		return
+	}
+	defer syscall.CloseHandle(syscall.Handle(snapshot))
+
+	var processEntry processEntry32
+	processEntry.dwSize = uint32(unsafe.Sizeof(processEntry))
+	ok, _, e1 := Process32First.Call(snapshot, uintptr(unsafe.Pointer(&processEntry)))
+	if ok == 0 {
+		err = fmt.Errorf("Process32First: %v", e1)
+		return
+	}
+
+	for {
+		if processEntry.th32ProcessID == uint32(pid) {
+			pe = &processEntry
+			return
+		}
+
+		ok, _, e1 = Process32Next.Call(snapshot, uintptr(unsafe.Pointer(&processEntry)))
+		if ok == 0 {
+			err = fmt.Errorf("Process32Next: %v", e1)
+			return
+		}
+	}
+}
+
+func getppid() (pid int, err error) {
+	pe, err := getProcessEntry(os.Getpid())
+	if err != nil {
+		return
+	}
+
+	pid = int(pe.th32ParentProcessID)
+	return
+}
+
+// StartedByExplorer returns true if the program was invoked by the user double-clicking
+// on the executable from explorer.exe
+//
+// It is conservative and returns false if any of the internal calls fail.
+// It does not guarantee that the program was run from a terminal. It only can tell you
+// whether it was launched from explorer.exe
+func StartedByExplorer() bool {
+	ppid, err := getppid()
+	if err != nil {
+		return false
+	}
+
+	pe, err := getProcessEntry(ppid)
+	if err != nil {
+		return false
+	}
+
+	name := syscall.UTF16ToString(pe.szExeFile[:])
+	return name == "explorer.exe"
+}