schemachangerccl: limit number of stages tested for MR

Previously, this test was timing out frequently because of the number of
stages that we were testing causing it to hit the test timeout. This
patch reduces the number of stages tested on MR for declarative schema
changes during backup / restore. This patch also adjusts timeout waiting
for schema changes to allow for stress runs for testing.

Release note: None
Fixes: #154993
Fixes: #155137
Fixes: #154786
Fixes: #152076
Fixes: #155327
Fixes: #154805
Fixes: #155147

Author: fqazi

pkg/sql/schemachanger/sctest/backup.go

@@ -129,7 +129,7 @@ const skipRate = .6
 
 // Stop once max stages has been hit.
 const maxStagesToTest = 8
-const maxStagesToTestMultiRegion = 6
+const maxStagesToTestMultiRegion = 4
 
 // shouldSkipBackup samples about 60% of total stages or up to
 // max stages.

pkg/sql/schemachanger/sctest/framework.go

@@ -965,6 +965,14 @@ func waitForSchemaChangesToSucceed(t *testing.T, tdb *sqlutils.SQLRunner) {
 }
 
 func waitForSchemaChangesToFinish(t *testing.T, tdb *sqlutils.SQLRunner) {
+	// Wait longer on stress for schema changes.
+	if skip.Stress() {
+		old := tdb.SucceedsSoonDuration
+		tdb.SucceedsSoonDuration = time.Minute * 2
+		defer func() {
+			tdb.SucceedsSoonDuration = old
+		}()
+	}
 	tdb.CheckQueryResultsRetry(
 		t, schemaChangeWaitQuery(`('succeeded', 'failed')`), [][]string{},
 	)