Remove the sonar-scanner-cli zip from the Image

[hansingt]

Currently, the Dockerfile downloads the sonar-scanner-cli from sonarsource.com and unzips it to /usr/bin/sonar-scanner. But it does not delete the original zip file. Thus, the image size is needlessly increased and the image is not "clean" as well.

A simple rm sonar-scanner-cli-${SONAR_SCANNER_VERSION}-linux.zip within the Dockerfile would resolve this.