Inconsistent analyze_string return values

[KevinHock]

So right now the private_key plugin returns a dictionary of the form {'filename':PotentialSecret}, whereas the high_entropy_strings plugin returns a dictionary of the form {PotentialSecret.__hash()__: PotentialSecret}. We should change this to be the same, I lean towards the {PotentialSecret.__hash()__: PotentialSecret} because I think the rest of the code assumes this. So e.g.

-            output[filename] = PotentialSecret(
+            secret = PotentialSecret(
                 self.secret_type,
                 filename,
                 line_num,
                 string,
             )
+            output[secret] = secret