testSystemTools: apply root-check to more systems

Brad Kingrequested to merge
brad.king/kwsys:SystemTools-test-root-check into master

The TestFileAccess test fails on FreeBSD (probably others) with this message:

TestFileAccess incorrectly indicated that this is a writable file

if the test is run as root; apply the same cop-out as on Linux and don't run it when testing as root.

Patch-by: @adridg

Merge request reports