xfstests: set umask to avoid spurious generic/314 test failures

xfstests: set umask to avoid spurious generic/314 test failures

Generic/314 can fail when the group write file mode bit for "subdir" does not
match that found in the golden output, as has been seen in ext4 regression
testing.  It appears that the golden output for generic/314 was taken on a
system where the $qa_user's umask cleared that mode bit - most likely, where
the umask was 022.  Depending upon the distro, it's not uncommon for a user's
default umask to have a different value, such as 002.  When that's the case,
we get a false negative failure when the group write mode bit for "subdir" is
not cleared.  This failure is unrelated to the value of the SGID mode bit
that is the object of this test.

We could either require that $qa_user's account be configured in advance with
a umask of 022, or explicitly set a umask value compatible with the golden
output when creating "subdir".  The latter option is more robust.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>