Change result evidence naming

This MR changes the names of the evidences saved in the result as follows

• logz -> log_evidence
• noise_logz -> log_noise_evidence
• logzerr -> log_evidence_err

I also fixed a bug where the use_ratio flag wasn't being correctly identified.

assigned to @colm.talbot

assigned to @gregory.ashton

merged

mentioned in commit d26e9a0f