try using non-root user

Dockerfile

@@ -1,5 +1,10 @@
 FROM williamyeh/ansible:ubuntu16.04
 
+ARG user=jenkins
+ARG group=jenkins
+ARG uid=1000
+ARG gid=1000
+
 RUN apt-get update -y && \
   apt-get install -y git unzip
 
@@ -11,6 +16,10 @@ ARG TERRAFORM_VERSION=0.11.1
 ADD https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip /tmp/terraform_${TERRAFORM_VERSION}_linux_amd64.zip
 RUN unzip /tmp/terraform_${TERRAFORM_VERSION}_linux_amd64.zip -d /usr/local/bin
 
+# https://github.com/jenkinsci/docker/blob/ca17603a0ff907728201f6285a4182020b277b87/Dockerfile#L18-L19
+RUN groupadd -g ${gid} ${group} && \
+      useradd -u ${uid} -g ${gid} -m -s /bin/bash ${user}
+USER ${user}
 # required for Packer
 # https://groups.google.com/d/msg/packer-tool/92wq5kYOvto/kkzoASaMAQAJ
-ENV USER root
+ENV USER ${user}

Jenkinsfile

@@ -14,7 +14,7 @@ pipeline {
           image '18fgsa/devsecops-builder'
           alwaysPull true
           // https://support.cloudbees.com/hc/en-us/articles/218583777-How-to-set-user-in-docker-image-
-          args '-u root'
+          args '-u jenkins:jenkins'
         }
       }
       environment {