Use file check to dynamically constantize analyzer

Exceptions must not be used to control code flow. Therefore, the rescue
block has been replaced by a proper file lookup. The new code is backed
by an appropriate RSpec unit test.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Set uk-ogl license to open

The uk-ogl license, mainly used by data.gov.uk was falsely seen as a
closed license. With this change, data.gov.uk should have a much better
result in the license metric.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>