Improve error resilience and handling

Timeouts are now handled correctly and the Runner automatically
creates the execution environment if it could not be found in
Poseidon. The runner is deleted locally if Poseidon returns
a bad request error.

spec/lib/runner/strategy/poseidon_spec.rb

@@ -16,11 +16,26 @@ describe Runner::Strategy::Poseidon do
       let(:response_status) { 400 }
 
       it 'raises an error' do
+        allow(Runner).to receive(:destroy).with(runner_id)
         expect { action.call }.to raise_error(Runner::Error::BadRequest, /#{error_message}/)
       end
     end
   end
 
+  # Only #copy_files and #execute_command destroy the runner locally in case
+  # of a BadRequest (400) response.
+  shared_examples 'BadRequest (400) destroys local runner' do
+    context 'when Poseidon returns BadRequest (400)' do
+      let(:response_body) { {message: error_message}.to_json }
+      let(:response_status) { 400 }
+
+      it 'destroys the runner locally' do
+        expect(Runner).to receive(:destroy).with(runner_id)
+        expect { action.call }.to raise_error(Runner::Error::BadRequest)
+      end
+    end
+  end
+
   # All requests handle a Unauthorized (401) response the same way.
   shared_examples 'Unauthorized (401) error handling' do
     context 'when Poseidon returns Unauthorized (401)' do
@@ -193,6 +208,7 @@ describe Runner::Strategy::Poseidon do
     end
 
     include_examples 'BadRequest (400) error handling'
+    include_examples 'BadRequest (400) destroys local runner'
     include_examples 'Unauthorized (401) error handling'
     include_examples 'NotFound (404) error handling'
     include_examples 'InternalServerError (500) error handling'
@@ -247,6 +263,7 @@ describe Runner::Strategy::Poseidon do
     end
 
     include_examples 'BadRequest (400) error handling'
+    include_examples 'BadRequest (400) destroys local runner'
     include_examples 'Unauthorized (401) error handling'
     include_examples 'NotFound (404) error handling'
     include_examples 'InternalServerError (500) error handling'