CI improvements: add source tests in lxc environment and concurrent builds

[Matteo Nastasi]

This task has 2 goals:

- 1 -
Run concurrent builds from different repos/branches without race on shared resources.
 To achive this result we have moved all the source tests in a lxc sendbox to avoid concurrency problems with postgresql or redis,
enhanced local debian repositories to allow multiple series repos for each source repository/branch couple.

- 2 -
Use task_1 to activate continuous integration or "test on pull request" for our source repositories.

This part of the task is postponed because during the development we discover that although on paper jenkins jobs are able to manage multiple branches contemporarly, in fact their use is not feasible and a diffrent approach is required.

Probably a more fruitful approach could be a git monitor that drive and reconfigure jenkins when event happens on github with a new jenkins job for each repo+branch item.