roachprod: use csv when upserting virtual cluster metadata

Previously, we would run a query with `roachprod sql --format
json`. However, that makes this logic impossible to backport in the
23.1 release branch, since JSON support is not available there.

In this commit, we switch the format to CSV, making this behaviour
more widely supported across branches.

Epic: none

Release note: None

pkg/roachprod/install/cockroach.go

@@ -13,7 +13,7 @@ package install
 import (
 	"context"
 	_ "embed" // required for go:embed
-	"encoding/json"
+	"encoding/csv"
 	"fmt"
 	"net/url"
 	"os"
@@ -1255,7 +1255,7 @@ func (c *SyncedCluster) upsertVirtualClusterMetadata(
 ) (int, error) {
 	runSQL := func(stmt string) (string, error) {
 		results, err := startOpts.KVCluster.ExecSQL(ctx, l, startOpts.KVCluster.Nodes[:1], "", 0, []string{
-			"--format", "json", "-e", stmt,
+			"--format", "csv", "-e", stmt,
 		})
 		if err != nil {
 			return "", err
@@ -1268,10 +1268,6 @@ func (c *SyncedCluster) upsertVirtualClusterMetadata(
 	}
 
 	virtualClusterIDByName := func(name string) (int, error) {
-		type tenantRow struct {
-			ID string `json:"id"`
-		}
-
 		query := fmt.Sprintf(
 			"SELECT id FROM system.tenants WHERE name = '%s'", startOpts.VirtualClusterName,
 		)
@@ -1281,16 +1277,17 @@ func (c *SyncedCluster) upsertVirtualClusterMetadata(
 			return -1, err
 		}
 
-		var tenants []tenantRow
-		if err := json.Unmarshal([]byte(existsOut), &tenants); err != nil {
-			return -1, fmt.Errorf("failed to unmarshal system.tenants output: %w\n%s", err, existsOut)
+		rows, err := csv.NewReader(strings.NewReader(existsOut)).ReadAll()
+		if err != nil {
+			return -1, fmt.Errorf("failed to parse system.tenants output: %w\n%s", err, existsOut)
 		}
 
-		if len(tenants) == 0 {
+		records := rows[1:] // skip header
+		if len(records) == 0 {
 			return -1, nil
 		}
 
-		n, err := strconv.Atoi(tenants[0].ID)
+		n, err := strconv.Atoi(records[0][0])
 		if err != nil {
 			return -1, fmt.Errorf("failed to parse virtual cluster ID: %w", err)
 		}