Add some exit codes

The external provider needs a simple way to indicate certain types of
errors. Duplicate error and not found error are such an example.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

runner/providers/external/execution/exit_codes.go

@@ -0,0 +1,26 @@
+package execution
+
+import (
+	"errors"
+
+	gErrors "github.com/cloudbase/garm/errors"
+)
+
+const (
+	// ExitCodeNotFound is an exit code that indicates a Not Found error
+	ExitCodeNotFound int = 30
+	// ExitCodeDuplicate is an exit code that indicates a duplicate error
+	ExitCodeDuplicate int = 31
+)
+
+func ResolveErrorToExitCode(err error) int {
+	if err != nil {
+		if errors.Is(err, gErrors.ErrNotFound) {
+			return ExitCodeNotFound
+		} else if errors.Is(err, gErrors.ErrDuplicateEntity) {
+			return ExitCodeDuplicate
+		}
+		return 1
+	}
+	return 0
+}

runner/providers/external/external.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"os/exec"
 
 	"github.com/cloudbase/garm/config"
 	garmErrors "github.com/cloudbase/garm/errors"
@@ -107,7 +108,11 @@ func (e *external) DeleteInstance(ctx context.Context, instance string) error {
 
 	_, err := garmExec.Exec(ctx, e.execPath, nil, asEnv)
 	if err != nil {
-		return garmErrors.NewProviderError("provider binary %s returned error: %s", e.execPath, err)
+		var exitErr exec.ExitError
+		if !errors.As(err, &exitErr) || exitErr.ExitCode() != execution.ExitCodeNotFound {
+			return garmErrors.NewProviderError("provider binary %s returned error: %s", e.execPath, err)
+		}
+
 	}
 	return nil
 }