Disable 'repository check' feature in 8.7.0

It still causes too many false alarms.

CHANGELOG

@@ -53,7 +53,7 @@ v 8.7.0 (unreleased)
   - Add links to CI setup documentation from project settings and builds pages
   - Display project members page to all members
   - Handle nil descriptions in Slack issue messages (Stan Hu)
-  - Add automated repository integrity checks
+  - Add automated repository integrity checks (OFF by default)
   - API: Expose open_issues_count, closed_issues_count, open_merge_requests_count for labels (Robert Schilling)
   - API: Ability to star and unstar a project (Robert Schilling)
   - Add default scope to projects to exclude projects pending deletion

db/migrate/20160421130527_disable_repository_checks.rb

+class DisableRepositoryChecks < ActiveRecord::Migration
+  def up
+    change_column_default :application_settings, :repository_checks_enabled, false 
+    execute 'UPDATE application_settings SET repository_checks_enabled = false'
+  end
+
+  def down
+    change_column_default :application_settings, :repository_checks_enabled, true    
+    execute 'UPDATE application_settings SET repository_checks_enabled = true'
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160419120017) do
+ActiveRecord::Schema.define(version: 20160421130527) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -77,7 +77,7 @@ ActiveRecord::Schema.define(version: 20160419120017) do
     t.string   "akismet_api_key"
     t.boolean  "email_author_in_body",              default: false
     t.integer  "default_group_visibility"
-    t.boolean  "repository_checks_enabled",         default: true
+    t.boolean  "repository_checks_enabled",         default: false
     t.integer  "metrics_packet_size",               default: 1
     t.text     "shared_runners_text"
   end

doc/administration/repository_checks.md

 # Repository checks
 
 >**Note:**
-This feature was [introduced][ce-3232] in GitLab 8.7.
+This feature was [introduced][ce-3232] in GitLab 8.7. It is OFF by
+default because it still causes too many false alarms.
 
 Git has a built-in mechanism, [git fsck][git-fsck], to verify the
 integrity of all data commited to a repository. GitLab administrators