Component Isolation v4

This another version of the component isolation work. The big differences are:

* To make the review easier, only the fundamental infrastructure regarding distros, packages and test environments are present;
* A client site library and command line utilities (`autotest-distro-def-create` and `autotest-distro-def-view`) are introduced. This serves the purpose of creating so called "Autotest Distro Definition" files, which packs relevant information on some characteristics and all software of a given distro;
* A frontend site utility (`autotest-distro-def-load`) that loads the distro definition files into the server database.

Once this makes its way in, I'll be adding the results parsing and visualization pieces.