Skip a test that fails when run as root.

Found by: Jeff Hemmelgarn <jeffhemme{_AT_}gmail.com>

* subversion/tests/cmdline/wc_tests.py
  (is_posix_os_and_not_root): New.
  (status_with_inaccessible_wc_db): Skip if root.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1583580 13f79535-47bb-0310-9956-ffa450edef68