pyfaf: return solutions in JSON

A solution is still a part of the message and JSON solution has
been added. The JSON solution is returned in a list because we can
expect that a single problem can have more solutions.

Closes #186

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Signed-off-by: Richard Marko <rmarko@redhat.com>