Install ncurses headers in the Jenkins machine's setup script

@johnsullivan made a devshell.py fix that requires the Python readline package
to be installed. By installing the readline dependency ncurses-dev on Jenkins
we can put readline in requirements.txt so that all devs will automatically
get it as part of their setup process.

Test Plan: On the Jenkins machine, ran the following commands without error:
```
sudo apt-get update
sudo apt-get install ncurses-dev
pip install readline
```

Auditors: johnsullivan