GRADLE-2587 Provide option to fork Sonar analysis

Improved SonarRunner task class to allow analysis in separate process
Added unit and smoke integration test for forked sonar analysis
GRADLE-2587 Documentation

Updated sonar runner plugin user guide page
Updated SonarRunner javadoc
GRADLE-2587 SonarQube refactoring

Enabled SonarRunner tasks fork mode
Added sonarRunner configuration to configure classpath
Added SonarRunnerRootExtension
Refactored smoke integration test to use a newer version of SonarQube server (4.3.2)
avoid sleeps in SonarRunnerSmokeIntegrationTest

+review REVIEW-5170
don't use fix port in SonarRunnerSmokeIntegrationTest

+review REVIEW-5170