Revert "Merge pull request #12 from autotest/provider-libs"

This reverts commit c6c5aa5719c1afd7d788b45b542c009cfb2c9590, reversing
changes made to 9ca076451044351e8c255465d33d0345f145993c.
attach_detach_interface: Check for required utility

When running the 'bridge' tests, the code needs to check for the used
'brctl' utility before using it; otherwise, the tests will FAIL.