Fix several issues in Vagrant provisioning (#1046)

* Fixes to Vagrantfile

scripts/install_docker.sh

@@ -4,8 +4,8 @@
 # per: https://docs.docker.com/engine/installation/linux/debian/#install-docker-ce
 
 # Install packages to allow apt to use a repository over HTTPS
-sudo apt-get install -y \
-    python-pip
+sudo DEBIAN_FRONTEND=noninteractive apt-get install -y \
+    python-pip \
     apt-transport-https \
     ca-certificates \
     curl \
@@ -25,14 +25,14 @@ sudo add-apt-repository \
 sudo apt-get update
 
 # Install the latest version of Docker
-sudo apt-get install -y docker-ce
+sudo DEBIAN_FRONTEND=noninteractive apt-get install -y docker-ce
 
 # Add user to the docker group
 # Warning: The docker group grants privileges equivalent to the root user. 
-sudo usermod -aG docker ubuntu
+sudo usermod -aG docker ${USER}
 
 # Configure Docker to start on boot
 sudo systemctl enable docker
 
 # Install docker-compose
-sudo pip install docker-compose
+pip install docker-compose