Following up on r1618138, fix Ruby test failure.

* subversion/bindings/swig/ruby/test/test_ra.rb:
  (test_uuid): With the introduction of the instance IDs, the string
    representation of the 'db/uuid' contents does not really have to match
    the result of the svn_ra_get_uuid2() calls.  Fix the failure by entirely
    avoiding the necessity to parse the 'db/uuid' file.  This is nothing more
    than a smoke test, so we might as well compare Svn::Ra::Session.uuid and
    Svn::Fs::FileSystem.uuid.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618177 13f79535-47bb-0310-9956-ffa450edef68