Slot layout configuration makes no sense now
The current slot_layout setup is implemented as a special parameter to glidein_startup.sh.This does not make sense for several reasons:
- glidein_startup.sh just converts it to an attribute... it makes not special use of it
- the decision of what kind of layout a glidein should have is really a FE decision... and, luckily, the FE can indeed overwrite that attribute now
We should thus get rid of this special treatment of the slot layout, and just make it a regular attribute.
And document how a FE influences it.