Improve utils test: test_file_lock_delete_with_acquire

Update the test test_file_lock_delete_with_acquire to acquire a second
FileLock instance using the same file path, with the previous lock still
held which would succeed, since there is no way to avoid the lock file
from getting deleted by an external entity.
Add utils test: test_file_lock_dir_without_permissions .

Add test_file_lock_dir_without_permissions, which test creating a lock
file in a directory with no permissions.
Use consistent file naming convention across tests.