Follow-up to r1618848: Fix svnadmin tests.

* subversion/tests/cmdline/svntest/main.py
  (svnfsfs_binary): Look up at new location.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618854 13f79535-47bb-0310-9956-ffa450edef68