Refactoring of base ui class for tests.

* Removed unused imports;
* Removed screenshot method for failed tests (skipped tests were
  causing some issues with the logic). Will revisit it some other
  time;
* Configuration values are read only once using the setUpClass method;
* Since we do want a new browser instance for every test, the setUp
  method was not removed;
* Added a tearDown method to handle closing the browser;
Added a generic search method to base ui class.

Since all or at least most objects have a search box, I have added a
generic search method that will be exposed to all ui classes.
Updated UI tests for Operating Systems.

* Updated several methods for the UI operating system class to use
  search method, since this is the best way to make sure that we can
  locate a record due to pagination;
* If web elements are not found, raise exception;
* Skipping several tests due to a Foreman issue related to searching
  operating systems via the UI;