[IMP] runbot: permit to qualify build errors

[d-fence]

Identifying build errors by fingerprint is not enough. Most of the times we want to link build errors based on some criteria.

With this commit, a build error can be qualified by using regular expressions that will extract informations.

Those informations will be stored in a jsondict field. That way, we can find simmilar build errors when they share some qualifiers.

To extract information, the regular expression must use named group patterns.

e.g:
^Tour (?P<tour_name>\w+) failed at step (?P<tour_step>.+)

The above regular expression should extract the tour name and tour step from a build error and store them like:
{ "tour_name": "article_portal_tour", "tour_step": "clik on 'Help'" }

The field can be queried to find similar errors. Also, a button is added on the Build Error Form to search for errors that share the same qualifiers.

TODO

• Decide if we can select the source field or if it will be always based on the content field
• Decide if we store the regex_id alongside with the qualifier (probably not a good idea)