Run stack_check after DB migrations and seeds (#453)

Running the stack_check before the initial DB setup fails, as it waits for the database schema to be current (Sequel::Migrator.is_current?).

jobs/cloud_controller_ng/templates/pre-start.sh.erb

@@ -142,14 +142,14 @@ function main {
   start_bosh_dns_or_consul
   setup_directories
   <% if spec.bootstrap && p('cc.run_prestart_migrations') %>
-  stack_check
   perform_migration
   seed_db
     <% if p('cc.database_encryption.skip_validation') %>
     echo "Skipping DB encryption validation"
     <% else %>
     validate_encryption_keys
     <% end %>
+  stack_check
   <% else %>
   echo "Skipping DB migrations and seeds"
   <% end %>