selftests/damon/sysfs.py: stop DAMON for dumping failures

selftests/damon/sysfs.py: stop DAMON for dumping failures

Commit 4ece01897627 ("selftests/damon: add python and drgn-based DAMON
sysfs test") in mm-stable tree introduced sysfs.py that runs drgn for
dumping DAMON status.  When the DAMON status dumping fails for reasons
including drgn uninstalled environment, the test fails without stopping
DAMON.  Following DAMON selftests that assumes DAMON is not running when
they executed therefore fail.  Catch dumping failures and stop DAMON for
that case.

Link: https://lkml.kernel.org/r/20250722060330.56068-1-sj@kernel.org
Fixes: 4ece01897627 ("selftests/damon: add python and drgn-based DAMON sysfs test")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202507220707.9c5d6247-lkp@intel.com
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>