Merge pull request #158 from dealnews/slave_service_echo_fix

Remove echo debug line from slave service script
Install swarm-client 1.16

This is necessary to avoid compatibility issues with newer Jenkins
versions (e.g. see https://issues.jenkins-ci.org/browse/JENKINS-20138).
Merge pull request #162 from mark0n/swarmVersion

bump up default version of swarm client
Merge branch 'master' into production