Reorganize setup.py a little and add `--package-only` install option

[LoveIsGrief]

Hello,

This is realated to naparuba/shinken#1854 Feature request: --package-only option when installing

It is the implementation + a reorg of the setup.py code into functions. Furthermore it adds a Vagrantfile for easier testing of the installation via sudo pip install /vagrant.

A few things to mention:

• The order of the function definitions hasn't been optimized for readability
• The main function is now shorter in an attempt to make the logic more readable
• pip install -e . now works
• In order to fully install shinken after a pip install --install-option="--package-only" . a call to pip install --upgrade . should be made as it will check if shinken has already been installed
• pip install --upgrade shinken doesn't seem to have ever passed in the old is_update path, so this reorganized code doesn't either
• tests of setup.py are still manual but could be automated using vagrant (not done yet)

I'm very open to constructive criticism and wouldn't mind restructuring code or (if necessary) adding the tests using vagrant as mentioned above.

Cheers

[naparuba]

I'll look at conflicts.

[geektophe]

Hello,

This is quite interesting. Could you please rebase your branch so that it can be merged ?

Many thanks !