Hi - The easiest thing would be to appraoch the landlord and ask him if it were OK to add a shower hose/head to the wall. It would be there for him for other tennants then also. However, if not a suction cap may not be the best idea, they have a habit of giving up their suction when you least expect it!
If you cut a piece of 15mm plywood down to about 300mm a 150mm you can stick it to the wall with the construction adhesive shown below. put a dab of adhesive in each corner and press to the tiles for a minute or so until the board is self-supporting. It willbe necessary to paint the board first to prevent water getting into the timber.
The shower head can then be fixed to the timber and should you move a sharp scraper behind the adhesive dabs will get the timber off the wall. You will probably need to clean any surplus adhesive off the tiles with a hobby knife blade or a window scraper.
Link to Clearfix adhesive which is suitable for use even under water
https://www.diydoctor.org.uk/DIY-superst ... ve-c3.html Hope this helps. Do come back and let us know how you get on.