The configurations related to the "data_dir" are currently read at
module load time. This means that changes in the configuration between
module load time and changes to the settings (such as parsing an
additional config file) is never seen.

Since the avocado command line application parses extra configuration
files (given with `--config`) after the module is loaded, these extra
configuration files are never applied to the data_dir configuration.

There's one more issue with regards to the the settings usage: because
once references to the `settings` instance singleton are grabbed, they
will always point to the same settings objects. The data_dir unittests
exercise changes to the settings objects by replacing that
instance. So, let's refer to the settings using the full location
(module.attribute), which will always give back the "current" (be it
original or replaced) settings instance.
Signed-off-by: NCleber Rosa <crosa@redhat.com>