Gracefully handle the deletion of non-existing runners

lib/runner/strategy/poseidon.rb

@@ -101,6 +101,8 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Destroying runner at #{runner_url}" }
     response = self.class.http_connection.delete runner_url
     self.class.handle_error response unless response.status == 204
+  rescue Runner::Error::RunnerNotFound
+    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Runner not found, nothing to destroy" }
   rescue Faraday::Error => e
     raise Runner::Error::FaradayError.new("Request to Poseidon failed: #{e.inspect}")
   ensure

spec/lib/runner/strategy/poseidon_spec.rb

@@ -312,8 +312,15 @@ describe Runner::Strategy::Poseidon do
       end
     end
 
+    context 'when Poseidon returns NotFound (404)' do
+      let(:response_status) { 404 }
+
+      it 'raises an error' do
+        expect { action.call }.not_to raise_error(Runner::Error::RunnerNotFound)
+      end
+    end
+
     include_examples 'Unauthorized (401) error handling'
-    include_examples 'NotFound (404) error handling'
     include_examples 'InternalServerError (500) error handling'
     include_examples 'unknown response status error handling'
     include_examples 'Faraday error handling'