Regression test portability: EXPECT

Make sure test_expect_not_footer() and test_expect_footer() work on
non empty strings, otherwise it may produce errors such as in pgfid_feat.t
on NetBSD:
not ok 12 Got "" instead of ""

This a a missing bit from previosuly merged patchset:
 I9cb76ba863897126534c3808fb0c9e564659835f

BUG: 1129939
Change-Id: I2635b67deec9cf60295faab52e7421947b1f7bda
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/8576
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>