sciond: Fix TRC not found locally error logic (#3043)

The error handling for remote TRCs not found locally is brittle.
By simply checking the error message with `common.GetErrMsg`, catching
wrapped errors is not possible.

fixes #3037

go/sciond/internal/fetcher/fetcher.go

@@ -19,6 +19,7 @@ package fetcher
 import (
 	"bytes"
 	"context"
+	"strings"
 	"time"
 
 	"github.com/opentracing/opentracing-go"
@@ -204,7 +205,7 @@ func (f *fetcherHandler) buildReplyFromDB(ctx context.Context,
 	switch {
 	case ctx.Err() != nil:
 		return f.buildSCIONDReply(paths, req.MaxPaths, sciond.ErrorNoPaths), nil
-	case ignoreTrustNotFoundLocally && common.GetErrorMsg(err) == trust.ErrNotFoundLocally:
+	case ignoreTrustNotFoundLocally && f.isTrustNotFoundLocally(err):
 		return nil, nil
 	case err != nil:
 		return f.buildSCIONDReply(paths, req.MaxPaths, sciond.ErrorInternal), err
@@ -214,6 +215,10 @@ func (f *fetcherHandler) buildReplyFromDB(ctx context.Context,
 	return nil, nil
 }
 
+func (f *fetcherHandler) isTrustNotFoundLocally(err error) bool {
+	return err != nil && strings.Contains(err.Error(), trust.ErrNotFoundLocally)
+}
+
 // buildSCIONDReply constructs a fresh SCIOND PathReply from the information
 // contained in paths. Information from the topology is used to populate the
 // HostInfo field.