tests: Use explicit pkcs11 library in thread test
tests: Use explicit pkcs11 library in thread test

Previously, the system-installed opensc was used, but there is no
guarantee that it exists when running tests. Use the locally built
library, even though there will probably not be any slots.

Using softhsm causes a lot of failures as it looks like this is not well
handled in there.

mouse07410/OpenSC,LudovicRousseau/OpenSC,LudovicRousseau/OpenSC,fabled/OpenSC,mouse07410/OpenSC,mouse07410/OpenSC,fabled/OpenSC,fabled/OpenSC,metsma/OpenSC,philipWendland/OpenSC,metsma/OpenSC,OpenSC/OpenSC,dengert/OpenSC,fabled/OpenSC,OpenSC/OpenSC,philipWendland/OpenSC,LudovicRousseau/OpenSC,OpenSC/OpenSC,metsma/OpenSC,dengert/OpenSC,dengert/OpenSC,philipWendland/OpenSC