Move install pages out of main macaron routes (#13195)

* Move install pages out of main macaron loop

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update templates/post-install.tmpl

Co-authored-by: Lauris BH <lauris@nix.lv>

* remove prefetch

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/graceful/manager.go

@@ -31,7 +31,7 @@ const (
 //
 // If you add an additional place you must increment this number
 // and add a function to call manager.InformCleanup if it's not going to be used
-const numberOfServersToCreate = 3
+const numberOfServersToCreate = 4
 
 // Manager represents the graceful server manager interface
 var manager *Manager