Quarantine flaky tests

See issues:
https://gitlab.com/gitlab-org/quality/nightly/issues/70
https://gitlab.com/gitlab-org/quality/nightly/issues/72
https://gitlab.com/gitlab-org/quality/staging/issues/21
https://gitlab.com/gitlab-org/quality/staging/issues/31
https://gitlab.com/gitlab-org/quality/staging/issues/30
https://gitlab.com/gitlab-org/quality/staging/issues/26

qa/qa/specs/features/browser_ui/1_manage/project/create_project_spec.rb

 # frozen_string_literal: true
 module QA
-  context 'Manage', :smoke do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/nightly/issues/72
+  context 'Manage', :smoke, :quarantine do
     describe 'Project creation' do
       it 'user creates a new project' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)

qa/qa/specs/features/browser_ui/1_manage/project/view_project_activity_spec.rb

 # frozen_string_literal: true
 module QA
-  context 'Manage' do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/21
+  context 'Manage', :quarantine do
     describe 'Project activity' do
       it 'user creates an event in the activity page upon Git push' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)

qa/qa/specs/features/browser_ui/3_create/merge_request/squash_merge_request_spec.rb

 # frozen_string_literal: true
 module QA
-  context 'Create' do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/31
+  context 'Create', :quarantine do
     describe 'Merge request squashing' do
       it 'user squashes commits while merging' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)

qa/qa/specs/features/browser_ui/4_verify/ci_variable/add_ci_variable_spec.rb

 # frozen_string_literal: true
 module QA
-  context 'Verify' do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/30
+  context 'Verify', :quarantine do
     describe 'CI variable support' do
       it 'user adds a CI variable' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)

qa/qa/specs/features/browser_ui/6_release/deploy_key/add_deploy_key_spec.rb

 # frozen_string_literal: true
 module QA
-  context 'Release' do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/26
+  context 'Release', :quarantine do
     describe 'Deploy key creation' do
       it 'user adds a deploy key' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)

qa/qa/specs/features/browser_ui/6_release/deploy_key/clone_using_deploy_key_spec.rb

@@ -3,7 +3,8 @@
 require 'digest/sha1'
 module QA
-  context 'Release', :docker do
+  # Failure issue: https://gitlab.com/gitlab-org/quality/nightly/issues/70
+  context 'Release', :docker, :quarantine do
     describe 'Git clone using a deploy key' do
       def login
         Runtime::Browser.visit(:gitlab, Page::Main::Login)