DEV: correct parallel specs rake tasks

This used to work due to side effects.

`rake parallel:migrate` used to work very inconsistently and would only migrate
some of the databases.

This introduces the recommended change to db.yml so the correct database is
found based off TEST_ENV_NUMBER if for some reason we did not set it using
RAILS_DB

Also avoids a bunch of schema dumping which is not needed when migrating
parallel specs



DB number 1 is very odd cause for whatever reason parallel spec is not
setting it.

config/database.yml

@@ -16,10 +16,23 @@ development:
 # Warning: The database defined as "test" will be erased and
 # re-generated from your development database when you run "rake".
 # Do not set this db to the same as development or production.
+
+<%
+  test_db = ENV["RAILS_DB"]
+  if !test_db.present?
+    test_db = "discourse_test"
+
+    if num = ENV["TEST_ENV_NUMBER"]
+      num = num.presence || "1"
+      test_db += "_#{num}"
+    end
+  end
+%>
+
 test:
   prepared_statements: false
   adapter: postgresql
-  database: <%= ENV["RAILS_DB"] ? ENV["RAILS_DB"] : "discourse_test" %>
+  database: <%= test_db %>
   min_messages: warning
   pool: 5
   timeout: 5000

lefthook.yml

@@ -9,6 +9,8 @@ pre-commit:
       run: yarn eslint --ext .es6 -f compact {staged_files}
     yaml-syntax:
       glob: "*.{yaml,yml}"
+      # database.yml is an erb file not a yaml file
+      exclude: "database.yml"
       run: bundle exec yaml-lint {staged_files}
 
 commands: &commands

lib/tasks/db.rake

@@ -68,20 +68,23 @@ end
 
 # we need to run seed_fu every time we run rake db:migrate
 task 'db:migrate' => ['load_config', 'environment', 'set_locale'] do |_, args|
+
   ActiveRecord::Tasks::DatabaseTasks.migrate
 
+  if !Discourse.is_parallel_test?
     Rake::Task['db:_dump'].invoke
+  end
 
   SeedFu.seed(DiscoursePluginRegistry.seed_paths)
 
-  unless Discourse.skip_post_deployment_migrations?
+  if !Discourse.skip_post_deployment_migrations?
     puts
     print "Optimizing site icons... "
     SiteIconManager.ensure_optimized!
     puts "Done"
   end
 
-  if MultisiteTestHelpers.load_multisite?
+  if !Discourse.is_parallel_test? && MultisiteTestHelpers.load_multisite?
     system("RAILS_DB=discourse_test_multisite rake db:migrate")
   end
 end