mantle: math/rand -> crypto/rand

To appease golangci-lint:

```
Error: SA1019: rand.Read has been deprecated since Go 1.20 because
it shouldn't be used: For almost all use cases, [crypto/rand.Read]
is more appropriate.
```

mantle/platform/api/azure/api.go

@@ -16,8 +16,8 @@
 package azure
 
 import (
+	"crypto/rand"
 	"fmt"
-	"math/rand"
 	"os"
 	"strings"
 	"time"
@@ -27,10 +27,13 @@ import (
 	"github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/network/armnetwork"
 	"github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/resources/armresources"
 	"github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/storage/armstorage"
+	"github.com/coreos/pkg/capnslog"
 
 	"github.com/coreos/coreos-assembler/mantle/auth"
 )
 
+var plog = capnslog.NewPackageLogger("github.com/coreos/coreos-assembler/mantle", "platform/api/azure")
+
 type API struct {
 	azIdCred   *azidentity.DefaultAzureCredential
 	rgClient   *armresources.ResourceGroupsClient
@@ -116,7 +119,9 @@ func (a *API) SetupClients() error {
 
 func randomName(prefix string) string {
 	b := make([]byte, 5)
-	rand.Read(b)
+	if _, err := rand.Read(b); err != nil {
+		plog.Errorf("randomName: failed to generate a random name: %v", err)
+	}
 	return fmt.Sprintf("%s-%x", prefix, b)
 }
 

mantle/platform/machine/azure/cluster.go

@@ -15,9 +15,9 @@
 package azure
 
 import (
+	"crypto/rand"
 	"errors"
 	"fmt"
-	"math/rand"
 	"os"
 	"path/filepath"
 
@@ -35,7 +35,9 @@ type cluster struct {
 
 func (ac *cluster) vmname() string {
 	b := make([]byte, 5)
-	rand.Read(b)
+	if _, err := rand.Read(b); err != nil {
+		plog.Errorf("failed to generate a random vmname: %v", err)
+	}
 	return fmt.Sprintf("%s-%x", ac.Name()[0:13], b)
 }
 

mantle/platform/machine/esx/cluster.go

@@ -15,9 +15,9 @@
 package esx
 
 import (
+	"crypto/rand"
 	"errors"
 	"fmt"
-	"math/rand"
 	"os"
 	"path/filepath"
 
@@ -32,7 +32,9 @@ type cluster struct {
 
 func (ec *cluster) vmname() string {
 	b := make([]byte, 5)
-	rand.Read(b)
+	if _, err := rand.Read(b); err != nil {
+		plog.Errorf("failed to generate a random vmname: %v", err)
+	}
 	return fmt.Sprintf("%s-%x", ec.Name(), b)
 }