Catch errors in LoadBalancing::Host#online?

See merge request gitlab-org/gitlab-ee!5177

Prior to this commit it was possible for Host#online? to raise a
connection error when checking an already offline host. This could
happen because certain methods used for checking if a host is available
call the "connection" method, without catching any errors. As a result,
if this method raises then #online? would also raise. All of this could
lead to GitLab becoming unavailable depending on how many times it would
try to use this offline host.

To work around this we catch the errors that might be raised in
Host#online?. Unlike the code in LoadBalancing::LoadBalancer we don't
need to catch individual PG errors as we don't have to worry about
application errors. This means we only have to catch up to three errors:

1. ActionView::Template::Error (used inside views).

2. ActiveRecord::StatementInvalid (used basically everywhere outside of
   views).

3. PG::Error: used in some rare cases where Rails (for reasons unknown)
   doesn't wrap the original error.

Resolve "Remove disabled eslint rules from `spec/javascripts/pipelines/graph/linked_pipelines_mock_data.js`"

Closes #2690

See merge request gitlab-org/gitlab-ee!5170

Add note to troubleshoot pgbouncer failing to connect to pg due to missing auth cidr address

See merge request gitlab-org/gitlab-ee!4831

Merge two spec files issues_settings_spec.rb into one

See merge request gitlab-org/gitlab-ee!5164

Merge two board destroy service spec

See merge request gitlab-org/gitlab-ee!5166

Move cross_project_issuable_information_filter_spec.rb to ee dir

See merge request gitlab-org/gitlab-ee!5167

Renaming of "xlog" to "wal" for PostgreSQL 10

See merge request gitlab-org/gitlab-ee!4669

Adds Vuex store for security reports

See merge request gitlab-org/gitlab-ee!5155

* master: (171 commits)
  EE port of vuex-action-helper-correctly-fail
  Update CHANGELOG.md for 10.6.2
  Update CHANGELOG-EE.md for 10.6.2-ee
  Fix workhorse tests
  Gitlab-workhorse still needs RepoPath on Git HTTP
  Harmonize can-attach-file to match CE
  Add Gitlab::ExclusiveLease to ObjectStorage#use_file
  Fix promoting labels and milestones copy text
  QA: allow rspec files/options to be handled more consistently
  Replaces "Libre" => "Core"
  Be explicit about when yellow favicon is used
  Use a brand-new Repository when performing Geo sync to a temporary directory
  Remove EE-specific comments from CE
  Trigger wiki sync when enabled
  Fixes conflicts on 'lib/gitlab/ci/config.rb'
  Resolve conflict in spec/spec_helper.rb
  Resolve "Skip repository-changing events on Geo secondaries if the repository hasn't been backfilled yet"
  Make all workhorse gitaly calls opt-out, take 2
  Revert "Merge branch 'workhorse-gitaly-mandatory' into 'master'"
  Resolve application settings UI conflicts after ce-to-ee merge
  ...

They're both EE only:

* ee/spec/services/boards/destroy_service_spec.rb
* spec/services/boards/destroy_service_spec.rb

We got both:

* ee/spec/features/projects/settings/issues_settings_spec.rb
* spec/features/projects/settings/issues_settings_spec.rb

But they're not the same! Also fix the descriptions

EE port of vuex-action-helper-correctly-fail

See merge request gitlab-org/gitlab-ee!5162

[ci skip]

[ci skip]

Port of add-per-runner-job-timeout to EE

See merge request gitlab-org/gitlab-ee!4649

Add Gitlab::ExclusiveLease to ObjectStorage#use_file

See merge request gitlab-org/gitlab-ee!5158

CE upstream - 2018-03-28 12:06 UTC

Closes #5461

See merge request gitlab-org/gitlab-ee!5145

Fix promoting labels and milestones copy text

See merge request gitlab-org/gitlab-ee!4955

Add canary favicon -- EE merge edition

See merge request gitlab-org/gitlab-ee!5135

Harmonize can-attach-file to match CE

Closes gitlab-ce#43915

See merge request gitlab-org/gitlab-ee!5067

Docs: replaces "Libre" => "Core"

See merge request gitlab-org/gitlab-ee!5152

QA: allow rspec files/options to be handled more consistently

See merge request gitlab-org/gitlab-ee!5144

Resolve "Temporary repositories in Geo sync download are broken"

Closes #5485

See merge request gitlab-org/gitlab-ee!5150