Verify paths

I am starting this merge request, but I would like to hear from @mcatanzaro what you think. Note it is definitely not ready yet but almost there.

This merge request changes the database implementation to not be an abstract class anymore, this follows the path taken by the gnutls backend. Now it loads the default locations for the CA certificates provided by openssl. The file database is slightly changed to load the location using the openssl api.

It also enables back the unit tests for openssl. Note I had to skip some new tests that are not passing with openssl.

I also had to change some unit tests since it seems they changed from what we had on openssl. I need some information about this though. And fixing these will be a blocker to get this merged since gnutls unit tests are not passing with the changes.