Force install for Scalrpy deps that can break

Those packages may already be installed on the system, and Scalrpy has
a versioned requirement on them.

In order to have the install complete properly, we force installation
of those packages in the virtualenv (where they won't conflict with
system packages).
Release: 3.3.0
Merge pull request #43 from Scalr/release-3.3.0

Release 3.3.0