jenkins docker plugin in pipeline use -u flag, how is possible to not using
By default, when the user is not specified, docker lauches the container with the user defined in the dockerfile which if not specified is root.You can try to force the default user by passing it:
args '-u root:root -v /var/lib/jenkins/workspace/myworkspace:/tmp/' + ' -v /var/lib/jenkins/.ssh:/root/.ssh'