test: Fix memleak in test-token cleanup

test: Fix memleak in test-token cleanup

GCC's asan spotted this:
  Direct leak of 338 byte(s) in 13 object(s) allocated from:
      #0 0x7f54f03fee20 in malloc (/lib64/libasan.so.3+0xc6e20)
      #1 0x445e8c in p11_path_build ../common/path.c:222
      #2 0x4385bd in expand_tempdir ../common/test.c:334
      #3 0x43869c in p11_test_directory ../common/test.c:361
      #4 0x4033e3 in setup_temp ../trust/test-token.c:79