Update Vagrantfile - python2 rsa

[caos21]

Force reinstallation of python2 rsa

The problem:

vagrant@vagrant:~$ python -c "import rsa; print rsa.__version__"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/rsa/__init__.py", line 24, in <module>
    from rsa.key import newkeys, PrivateKey, PublicKey
  File "/usr/local/lib/python2.7/dist-packages/rsa/key.py", line 1
SyntaxError: Non-ASCII character '\xc3' in file /usr/local/lib/python2.7/dist-packages/rsa/key.py on line 1, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details

This problem also arises when running views.py from course APIs - ud388

I tried: apt upgrade, restart, and finally pip2 install --upgrade rsa unsuccessfully.

The solution is to force the reinstallation of python2 rsa module.
I propose to perform it in the Vagrantfile in this PR.