Some tests had failed on `sudo make test-all`, mainly because root can
access any files regardless of permission.  This change adds `skip`
guards into such tests.

Note that almost all tests in which `skip` guards is added, already have
"windows" guard.  This is because there is no support to avoid read
access by owner on Windows.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61758 b2dd03c8-39d4-4d8f-98ff-823fe69b080e