While following the simulation installation tutorial at http://docs.erlerobotics.com/simulation/configuring_your_environment in a minimal Trusty jail I found the following missing steps:
Prior to installation of MAVProxy:
sudo apt install python-libxml2 libxml2-dev libxslt1-dev
sudo pip install future
Later, I had to follow Gazebo install steps prior to compilation using catkin. Also, prior to catkin compilation,
sudo apt install ros-indigo-transmission-interface ros-indigo-joint-limits-interface wget
Posting just in case it may help someone in the future.