logging: report issues in rbdImage.DEKStore API with stacks

It helps to get a stack trace when debugging issues. Certain things are
considered bugs in the code (like missing attributes in a struct), and
might cause a panic in certain occasions.

In this case, a missing string will not panic, but the behaviour will
also not be correct (DEKs getting encrypted, but unable to decrypt).
Clearly logging this as a BUG is probably better than calling panic().

Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/util/util.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"math"
 	"os"
+	"runtime"
 	"strconv"
 	"strings"
 	"time"
@@ -333,3 +334,12 @@ func getKeys(m map[string]interface{}) []string {
 
 	return keys
 }
+
+// CallStack returns the stack of the calls in the current goroutine. Useful
+// for debugging or reporting errors. This is a friendly alternative to
+// assert() or panic().
+func CallStack() string {
+	stack := make([]byte, 2048)
+	_ = runtime.Stack(stack, false)
+	return string(stack)
+}