Added a test for use a different mirror that the last update
Fixed the usage of a different mirror that the last update

Use only `<cachedir>/<mirror>/<arch>/setup.ini` to fetch all packages.
Added a note for back compatibility break for cyg-apt version 2
Added a test for raise a deprecation warning when the `setup_ini` field is used
Removed duplicated code

Improved deprecated warning assertion
Added a deprecation warning when the `setup_ini` field is used
Merge pull request #31 from alquerci/fix/setup_ini_location

Fixed usage of a different mirror that the last update