Fix failing EE builds due to blacklisted Web connections

If unicorn_spec.rb were run before Elasticsearch specs, it would
disable all outbound network connections, which would prevent the
latter from being able to communicate with Elasticsearch in CI. To
fix this, we restore the original WebMock settings after finishing
the spec.

Closes #2507

spec/support/webmock.rb

 require 'webmock'
 require 'webmock/rspec'
 
-allowed = %w[elasticsearch registry.gitlab.com-gitlab-org-test-elastic-image]
+def webmock_setup_defaults
+  allowed = %w[elasticsearch registry.gitlab.com-gitlab-org-test-elastic-image]
 
-if ENV.has_key?('ELASTIC_URL')
+  if ENV.has_key?('ELASTIC_URL')
     url = URI.parse(ENV['ELASTIC_URL'])
     allowed << url.host
     allowed.uniq!
+  end
+
+  WebMock.disable_net_connect!(allow_localhost: true, allow: allowed)
 end
 
-WebMock.disable_net_connect!(allow_localhost: true, allow: allowed)
+webmock_setup_defaults

spec/unicorn/unicorn_spec.rb

@@ -62,7 +62,7 @@ describe 'Unicorn' do
   end
 
   after(:all) do
-    WebMock.disable_net_connect!(allow_localhost: true)
+    webmock_setup_defaults
     Process.kill('TERM', @unicorn_master_pid)
   end