Fresh clone and `install_externals.bash` fails on `cmake: command not found` about eta HOT 6 CLOSED

Also pkg-config is not found or present by default.
Also libblas-dev liblapack-dev should probably be installed as well.

from eta.

Here's a list of things I had to install on VMs in google cloud:

sudo apt-get update
sudo apt-get install python-pip
sudo apt-get install python-dev
sudo apt-get install build-essential
sudo pip install --upgrade pip
sudo pip install --upgrade virtualenv
sudo apt-get install unzip
sudo apt-get install cmake
sudo apt-get install pkg-config
sudo apt-get install cmake-data

from eta.

I suppose we should add as much as possible to install_externals.bash so that ETA install will work on the most bare bones linux machines possible

from eta.

from eta.

The stuff I put above was done manually outside of install_externals.bash. I will copy in and remove sudos where possible.

from eta.

Done in #52

from eta.