Shared office is messy to the point that I can't do any work, how to proceed? Four months in my postdoc and I feel the mess, up to the point that I can't further do any, any work in my office. Nothing. My passion, bioinformatics, is gone. 

An office with 12 students where just 8 should be, and plenty of disorganised stuff, people coming in and out, chatting, not very clean... I would say it's more similar to a bar than to a real work office. Almost all them work on the bench, so they come and go to the computer frequently.

I've been promised to get a new place in a 5 students office in about a month, but this has already a delay of 2 months since I should have moved there like 2 months ago. This is the reason to be in a limit situation.

What to do? My mentor knows almost nothing about this. He knows I'm waiting for the new place but thinks I'm doing well, when this is far from true.

I work in bioinformatics but seems my mentor thinks this is like kid games. I feel homeless moving through libraries trying to go ahead with my work.
To add another perspective: You write that everyone else is doing fine, and in fact is doing productive work. I know that people have very different working styles (in our department, all office space is 'flex-space', i.e., no-one (including full professors) has an 'own' office and people have very different preferences whether they want to sit in a more quiet place or a more social stting), and it can very well be the case that you are not productive in a setting where others are.

Nevertheless, I think you should consider the possibility that it is actually you who has the problem, not the setting that is the problem. If there is no easy solution (i.e., a different space for you), then, in fact, I guess it would be unreasonable to expect 11 people to adapt their working style rather than you (1 person). 

I do not mean this negative at all, but there are solutions to work in a busy place, like putting on headphones and the like. Have you considered such options?

Good luck!