[BUG] It's possible to run multiple tasks with the same ID

[AlexPykavy]

Steps to reproduce:

• Run curl -v -d '{\"id\": \"44923378-ac56-4870-a64c-e97aad95a0db\", \"name\": \"myapp\", \"executable\": \"sleep\", \"args\": [\"infinity\"]}' http://localhost:8080/tasks in PowerShell
• Run curl -v -d '{\"id\": \"44923378-ac56-4870-a64c-e97aad95a0db\", \"name\": \"myapp\", \"executable\": \"sleep\", \"args\": [\"infinity\"]}' http://localhost:8080/tasks in PowerShell

Expected behavior:

• The second requests fails

Actual behavior:

• The second request succeeds and the first process is orphaned :(