Consolidate common libraries in common role

Turns out that we have a number of roles that call for the same sorts
of system dependencies. Consolidate them into the common role so that
we don't repeat ourselves.

Also move python-dev to python2.7-dev as python-dev could be a moving
target.
Merge pull request #308 from craigtracey/consolidatelibs

Consolidate common libraries in common role