Currently you have to enter a URL like this to access SonarQube's web UI:
You want to be able to type no path (e.g., no "sonar") in the web browser. You want to just enter the hostname in the web browser and the port number of the SonarQube server. What should you do?
Go to the conf directory [that is a sibling] with the sonar.properties file. Find the "context" stanza. It will have a string "sonar.web.context". Comment it out. By default it will be "/".
To learn more, see this posting.