Graceful: Xorm, RepoIndexer, Cron and Others (#9282)

* Change graceful to use a singleton obtained through GetManager instead of a global.
* Graceful: Make TestPullRequests shutdownable
* Graceful: Make the cron tasks graceful
* Graceful: AddTestPullRequest run in graceful ctx
* Graceful: SyncMirrors shutdown
* Graceful: SetDefaultContext for Xorm to be HammerContext
* Avoid starting graceful for migrate commands and checkout
* Graceful: DeliverHooks now can be shutdown
* Fix multiple syncing errors in modules/sync/UniqueQueue &  Make UniqueQueue closable
* Begin the process of making the repo indexer shutdown gracefully

integrations/auth_ldap_test.go

@@ -5,6 +5,7 @@
 package integrations
 
 import (
+	"context"
 	"net/http"
 	"os"
 	"strings"
@@ -147,7 +148,7 @@ func TestLDAPUserSync(t *testing.T) {
 	}
 	defer prepareTestEnv(t)()
 	addAuthSourceLDAP(t, "")
-	models.SyncExternalUsers()
+	models.SyncExternalUsers(context.Background())
 
 	session := loginUser(t, "user1")
 	// Check if users exists
@@ -206,7 +207,8 @@ func TestLDAPUserSSHKeySync(t *testing.T) {
 	}
 	defer prepareTestEnv(t)()
 	addAuthSourceLDAP(t, "sshPublicKey")
-	models.SyncExternalUsers()
+
+	models.SyncExternalUsers(context.Background())
 
 	// Check if users has SSH keys synced
 	for _, u := range gitLDAPUsers {