remove unnecessary spam from the docker exec command line#51

jcarrothers-sap wants to merge 2 commits intojenkinsci:masterjenkinsci/docker-custom-build-environment-plugin:masterfrom

jcarrothers-sap:trimDockerExecCmdLengthjcarrothers-sap/docker-custom-build-environment-plugin:trimDockerExecCmdLengthCopy head branch name to clipboard