Add Scalrpy 2 (Scalr 5.1) support

Installation procedures, calling conventions, as well as arguments have
changed.
Launch rrdcached with settings Scalrpy recognizes

The Scalrpy plotter starts rrdcached on its own if it doesn't find
it running. So that we don't end up with two rrdached processes, we
configure rrdcached so that it plays nice with what Scalrpy expects.
Release: 6.5.0
Merge pull request #66 from Scalr/release-6.5.0

Release 6.5.0