Flaky integration test

[hasit]

Running cluster.sh script in branch release/v0.5.0 on my machine fails the following test:

...
--- FAIL: TestIntegration_NodesJoinOrLeftDuringQuery (16.71s)
    olric_test.go:110: A new cluster member has been created: 127.0.0.1:33651
    olric_test.go:110: A new cluster member has been created: 127.0.0.1:42925
    integration_test.go:48: Wait for 1 second before inserting keys
    olric_test.go:110: A new cluster member has been created: 127.0.0.1:35837
    integration_test.go:71: Fetch all keys
    olric_test.go:110: A new cluster member has been created: 127.0.0.1:33221
    integration_test.go:86: Shutdown one of the nodes: 127.0.0.1:42925
    integration_test.go:91: Wait for "NodeLeave" event propagation
    olric_test.go:110: A new cluster member has been created: 127.0.0.1:35239
    integration_test.go:81: 
        	Error Trace:	integration_test.go:81
        	Error:      	Received unexpected error:
        	            	key not found
        	            	github.com/buraksezer/olric.init
        	            		/home/hm/fluxninja/olric/olric.go:70
        	            	runtime.doInit
        	            		/usr/local/go/src/runtime/proc.go:6506
        	            	runtime.doInit
        	            		/usr/local/go/src/runtime/proc.go:6483
        	            	runtime.main
        	            		/usr/local/go/src/runtime/proc.go:233
        	            	runtime.goexit
        	            		/usr/local/go/src/runtime/asm_amd64.s:1598
        	Test:       	TestIntegration_NodesJoinOrLeftDuringQuery
<nil>
...