Reduce peak memory consumption of the new fs-fs-fuzzy-test.

* subversion/tests/libsvn_fs_fs/fs-fs-fuzzy-test.c
  (fuzzing_1_byte_test): Re-open the repos in every operation.
                         That's ~10% runtime overhead but gives
                         flat memory usage.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1623369 13f79535-47bb-0310-9956-ffa450edef68