Prepare a default minimal test suite

We need to implement a minimal package integrity test suite that should be applied to any packages by default:

* Package can be installed: all dependencies are present, no conflicts happening.
* All shared libraries required by package binaries are installed as dependencies.
* Every symlink from a package points to an existent file.
* So-libraries don't have a trailing colon in RPATH.

I propose creating a separate git repository for those tests and use it by default. Although those tests are useful in most cases, there should be a way to turn them off for a task.