Slow UITests

I see that some of the UITests (executed at least during `make check`) 
take rather long, one taking over 20 min for me, see below for details.

I'm not sure whether something fundamental could be improved to cut down 
on processing time (e.g., on a cursory glance, it looks to me that a 
single UITest sequentially spawns multiple soffice processes?), or 
whether the cure would be to split the longer-running UITests into 
smaller ones each doing fewer sub-tests so that multiple of those 
smaller tests will run in parallel (similar to how other CppunitTests or 
JunitTests have been split in the past).

But I would ask the authors/maintainers of those UITests to please do 
something appropriate to help reduce overall build time.

Edited output of elapsed wall-clock time for each of the UITests (which 
all succeeded) for me (running `for i in */UITest_*.mk; do (cd 
"$(dirname "$i")" && (time make -rs "$(basename "$i" .mk)"; echo $?)); 
done`):

   0m13.038s hide_cols
   0m13.080s range_name
   0m14.920s search_replace
   0m16.144s cui_dialogs
   0m20.515s math_demo
   0m25.939s conditional_format
   0m26.513s writerperfect_epubexport
   1m00.827s manual_tests
   1m45.238s impress_demo
   2m00.418s autofilter
   2m05.138s calc_demo
   3m31.141s demo_ui
   5m09.131s writer_demo
   9m37.676s writer_tests
  22m28.748s calc_tests