Change if statement in SearchEngine class

[mageirakos]

Motivation

We started off expanding the SearchEngine class to work for general documentation.
There is a piece of code left that fails to do this.
An extra if statement inside SearchEngine changes the corpus attribute of the search engine
unless we specifically change it's type attribute .

Modification

Change this if statement: https://github.com/rucio/donkeybot/blob/master/lib/bot/searcher/base.py#L157
and the SearchEngine class in general to not autotmatically set the type attribute as Documentation Search Engine.
Another idea is for Rucio Docs which use this search engine, they could be of type 'Rucio Docs Search Engine' thus the
if statement doesn't change but rather every line where we call/create the SearchEngine