LU-4703 tests: Add test to check setxattr fails when it should

LU-4703 tests: Add test to check setxattr fails when it should

Setxattr was not correctly checking permissions in all cases. This
adds a test to sanity to ensure that trying to set xattrs on a file
fails when it should.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Id95e13ec3bcbedb7cbb069c610d506d1f3d899a8
Reviewed-on: http://review.whamcloud.com/9508
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>