make slowcheck ineffective

[Mattia Verga]

During Fedora packaging we run 'make unitcheck slowcheck' to check the 
build results, but I've just realized that since some time in the output 
we had:

make: Nothing to be done for 'slowcheck'

Looking at LibreOffice Jenkins I see it there as well, BTW in LO jenkins 
I see that unitcheck has the same output, while in Fedora that part works...

Mattia