Force using system site packages in the virtualenv

Workaroung for sippable.com lack of support for the
--system-site-packages, as per
https://github.com/Shippable/support/issues/241
Add "-y" (--yes) option to apt-get commands

To allow running the script unattended in systems without that
default.
[FIX] pylint: Fix #143 - Message symbol 'print-statement' is already defined
Merge pull request #144 from vauxoo-dev/master-print-core-dev-moylop260

[FIX] pylint: Fix #143 - Message symbol 'print-statement' is already defined
Merge pull request #140 from dreispt/workaround-shippable-virtualenvs

Force using system site packages in the virtualenv
Merge remote-tracking branch 'upstream/master'