Add baseline Docker images for Amazon Linux and CentOS 7

_docker-images/gruntwork-amzn-linux-test/Dockerfile

@@ -0,0 +1,14 @@
+# TODO: Is it worth referencing a specific tag instead of latest?
+FROM amazonlinux:latest
+
+# Reduce Docker image size per https://blog.replicated.com/refactoring-a-dockerfile-for-image-size/
+# - The last line upgrades pip to the latest version.
+RUN yum update -y && \
+    yum upgrade -y && \
+    yum install -y \
+        jq \
+        rsyslog \
+        sudo \
+        vim \
+        wget && \
+        yum clean all

_docker-images/gruntwork-amzn-linux-test/README.md

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+# Gruntwork Amazon-Linux-Test Docker Image
+
+The purpose of this Docker image is to provide a pre-built Amazon Linux Docker image that has most of the libraries
+we would expect to be installed on the Amazon Linux AMI that would run in AWS. For example, we'd expect `sudo` in AWS,
+but it doesn't exist by default in Docker `amazonlinux:latest`.
+
+### Building and Pushing a New Docker Image to Docker Hub
+
+This Docker image should publicly accessible via Docker Hub at https://hub.docker.com/r/gruntwork/amazonlinux-test/. To build and
+upload it:
+
+1. `docker build -t gruntwork/amazonlinux-test:latest .`
+1. `docker push gruntwork/amazonlinux-test:latest`
+

_docker-images/gruntwork-centos-test/Dockerfile

@@ -0,0 +1,25 @@
+FROM centos:7
+
+# Reduce Docker image size per https://blog.replicated.com/refactoring-a-dockerfile-for-image-size/
+# - The last line upgrades pip to the latest version.
+RUN yum update -y && \
+    yum upgrade -y && \
+    yum install -y epel-release && \
+    yum install -y \
+        bind-utils \
+        python-pip \
+        rsyslog \
+        sudo \
+        vim \
+        wget && \
+        yum clean all
+
+# Install jq. Oddly, there's no RPM for jq, so we install the binary directly. https://serverfault.com/a/768061/199943
+RUN wget -O jq https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64 && \
+    chmod +x ./jq && \
+    cp jq /usr/bin
+
+# Install the AWS CLI per https://docs.aws.amazon.com/cli/latest/userguide/installing.html
+RUN pip install --upgrade pip && \
+    pip install --upgrade setuptools && \
+    pip install awscli --upgrade

_docker-images/gruntwork-centos-test/README.md

@@ -0,0 +1,14 @@
+# Gruntwork CentOS-Test Docker Image
+
+The purpose of this Docker image is to provide a pre-built CentOS 7 Docker image that has most of the libraries
+we would expect to be installed on the CentOS 7 AMI that would run in AWS. For example, we'd expect `sudo` in AWS,
+but it doesn't exist by default in Docker `centos:7`.
+
+### Building and Pushing a New Docker Image to Docker Hub
+
+This Docker image should publicly accessible via Docker Hub at https://hub.docker.com/r/gruntwork/centos-test/. To build and
+upload it:
+
+1. `docker build -t gruntwork/centos-test:7 .`
+1. `docker push gruntwork/centos-test:7`
+

_docker-images/gruntwork-ubuntu-test/Dockerfile

@@ -5,16 +5,17 @@ FROM ubuntu:16.04
 RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install --no-install-recommends -y \
     ca-certificates \
     curl \
+    dnsutils \
     jq \
     python-pip \
     rsyslog \
     software-properties-common \
     sudo \
     vim \
     wget && \
-    rm -rf /var/lib/apt/lists/* && \
-    pip install --upgrade setuptools && \
-    pip install --upgrade pip
+    rm -rf /var/lib/apt/lists/*
 
 # Install the AWS CLI per https://docs.aws.amazon.com/cli/latest/userguide/installing.html
-RUN pip install awscli --upgrade
+RUN pip install --upgrade setuptools && \
+    pip install --upgrade pip && \
+    pip install awscli --upgrade