Fix bug in cli.pp that tries to exec without full qualified path

When adding a user it gave me the following error: 

Error: Validation of Exec[safe-restart-jenkins] failed: 'java -jar /usr/share/jenkins/jenkins-cli.jar -s http://localhost:8080 safe-restart && /bin/sleep 10' is not qualified and no path was specified. Please qualify the command or specify a path. at /etc/puppet/modules/jenkins/manifests/cli.pp:51

This patch fixes that error.