tests/prime: more paranoia
tests/prime: more paranoia

- check the old contents first in check_bo
- drop all GEM handles for the re-import test

erikarn/intel-gpu-tools,dlespiau/intel-gpu-tools,chenxianqin/intel-gpu-tools,dlespiau/checkmate-test-igt,yipdw/intel-gpu-tools,chenxianqin/intel-gpu-tools,ChrisCummins/intel-gpu-tools,ChrisCummins/intel-gpu-tools,erikarn/intel-gpu-tools,rib/intel-gpu-tools,dlespiau/checkmate-test-igt,ChrisCummins/intel-gpu-tools,chenxianqin/intel-gpu-tools,tiagovignatti/intel-gpu-tools,erikarn/intel-gpu-tools,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,chenxianqin/intel-gpu-tools,dlespiau/checkmate-test-igt,tiagovignatti/intel-gpu-tools,dlespiau/checkmate-test-igt,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,rib/intel-gpu-tools,rib/intel-gpu-tools,mv0/intel-gpu-tools,tiagovignatti/intel-gpu-tools,dlespiau/intel-gpu-tools,tiagovignatti/intel-gpu-tools,yipdw/intel-gpu-tools,ChrisCummins/intel-gpu-tools,rib/intel-gpu-tools,mv0/intel-gpu-tools,dlespiau/intel-gpu-tools,erikarn/intel-gpu-tools