For config see https://docs.sonarqube.org/display/SCAN/Analyzing+with+SonarQube+Scanner
try with something like this
-Dsonar.projectBaseDir=/app -Dsonar.host.url=$SONAR_HOST_URL -Dsonar.login=$SONAR_AUTH_TOKEN -Dproject.settings=~/myproject.properties -Dsonar.projectKey=myproject
test with cmd = --help
One could mount conf to /opt/sonar/latest/conf/sonar-runner.properties