Fix tests for Runner#attach_to_execution

These tests were blocking because of the newly introduced
EventLoop. The messages sent to the EventLoop are now mocked
and the EventLoop isn't blocking anymore in the tests.

spec/lib/runner/strategy/docker_container_pool_spec.rb

@@ -264,7 +264,8 @@ describe Runner::Strategy::DockerContainerPool do
     # TODO: add tests here
 
     let(:command) { 'ls' }
-    let(:action) { -> { container_pool.attach_to_execution(command) } }
+    let(:event_loop) { Runner::EventLoop.new }
+    let(:action) { -> { container_pool.attach_to_execution(command, event_loop) } }
     let(:websocket_url) { 'ws://ws.example.com/path/to/websocket' }
   end
 end

spec/lib/runner/strategy/poseidon_spec.rb

@@ -292,7 +292,8 @@ describe Runner::Strategy::Poseidon do
     # TODO: add tests here
 
     let(:command) { 'ls' }
-    let(:action) { -> { poseidon.attach_to_execution(command) } }
+    let(:event_loop) { Runner::EventLoop.new }
+    let(:action) { -> { poseidon.attach_to_execution(command, event_loop) } }
     let(:websocket_url) { 'ws://ws.example.com/path/to/websocket' }
   end
 end

spec/models/runner_spec.rb

@@ -62,10 +62,13 @@ describe Runner do
   describe '#attach to execution' do
     let(:runner) { described_class.create }
     let(:command) { 'ls' }
+    let(:event_loop) { instance_double(Runner::EventLoop) }
 
     before do
       allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
       allow(strategy_class).to receive(:new).and_return(strategy)
+      allow(event_loop).to receive(:wait)
+      allow(Runner::EventLoop).to receive(:new).and_return(event_loop)
     end
 
     it 'delegates to its strategy' do