Refactor Ubuntu related classes

Move Ubuntu 12.04 code into dedicated package.

This is in preparation for different code for Ubuntu 14.04,
which is not part of this commit.
Disable USB autoconnect
Switch examples to CentOS 6.6

Still supports both Scientific Linux 6.x and CentOS 6.x.
Declare 1.6.0 for API changes

Recently refactored some of package ub into ub.rel1204.