setup_vagrant.sh: Idempotentialize PhantomJS config

Only try to install and configure PhantomJS
if there is no phantomjs directory in /usr/local/bin.

setup/setup_vagrant.sh

@@ -31,12 +31,17 @@ sudo apt-get install -y chrpath libssl1.0-dev libxft-dev && \
   sudo apt-get install -y libfreetype6 libfreetype6-dev && \
   sudo apt-get install -y libfontconfig1 libfontconfig1-dev
 
-# Install Phantom JS
-export PHANTOM_JS="phantomjs-2.1.1-linux-x86_64" && \
-  wget https://github.com/Medium/phantomjs/releases/download/v2.1.1/$PHANTOM_JS.tar.bz2 && \
-  tar xvjf $PHANTOM_JS.tar.bz2 && \
-  sudo mv $PHANTOM_JS /usr/local/share && \
-  sudo ln -sf /usr/local/share/$PHANTOM_JS/bin/phantomjs /usr/local/bin
+# Install PhantomJS
+echo 'Installing PhantomJS'
+if [ ! -d /usr/local/bin/phantomjs/ ]; then
+  export PHANTOM_JS="phantomjs-2.1.1-linux-x86_64" && \
+    wget https://github.com/Medium/phantomjs/releases/download/v2.1.1/$PHANTOM_JS.tar.bz2 && \
+    tar xvjf $PHANTOM_JS.tar.bz2 && \
+    sudo mv $PHANTOM_JS /usr/local/share && \
+    sudo ln -sf /usr/local/share/$PHANTOM_JS/bin/phantomjs /usr/local/bin
+else
+  echo 'PhantomJS is already installed and configured. skipping...'
+fi
 
 # required packages
 declare -A packages