Move T-0 to "Prevent updates to the primary"

Closes #743

See merge request gitlab-com/migration!186

Fix the criteria for an alert silence

See merge request gitlab-com/migration!183

Resolve "Add step to kill queue disabling loop after sidekiq is stopped"

Closes #752

See merge request gitlab-com/migration!189

Resolve "Update failover templates with proper script references"

Closes #756

See merge request gitlab-com/migration!188

fix list of domains for hostinfo

See merge request gitlab-com/migration!187

Address (some) feedback from 2018-08-02 failover attempt

Closes #753

See merge request gitlab-com/migration!176

bash3.2 compatibility for hostinfo

Closes #755

See merge request gitlab-com/migration!185

test ssh on proper host in production

See merge request gitlab-com/migration!182

fix references to script location

See merge request gitlab-com/migration!181

Critical typo fix

See merge request gitlab-com/migration!180

Make remote rails runner commands work much better

See merge request gitlab-com/migration!179

Sidekiq Monitor Script, Mailroom Stop, Sidekiq Pullmirror Shutdown script

Closes #722

See merge request gitlab-com/migration!165

More symlink fixes

See merge request gitlab-com/migration!175

Harden the scripts against symlinks

See merge request gitlab-com/migration!174

Structure only

See merge request gitlab-com/migration!171

Revert "Merge branch 'database_wrangler_automation' into 'master'"

See merge request gitlab-com/migration!172

This reverts merge request !170

Database wrangler automation

See merge request gitlab-com/migration!170