(#12412) Mark symbolic file modes test as pending on Windows

Previously, the test used hard-coded tmp file locations, and then
passed the posix style paths to puppet apply, which doesn't work on
Windows agents.

This commit refactors the test to use Host#tmpfile and Host#tmpdir`
methods, which requires using agents.each do |agent| style test.

Also, there are problems executing chmod 0000 path via Cygwin as the
resulting file always has at least 0400 permission. For now, I'm
marking the entire test as pending on Windows and will come back to
it.