fstests: filter redundant output by getfattr

When getfattr dumps values of all extended attributes (-d option),
it doesn't print empty extended attributes. e.g: user.name. But from
attr-2.4.48 this behavior is changed,  new getfattr prints
user.name="".

The {=""} will break the golden image, so filter the redundant =""
at the end if it has.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/097

@@ -30,7 +30,7 @@ _cleanup()
 
 getfattr()
 {
-	$GETFATTR_PROG --absolute-names "$@" |& _filter_test_dir
+	_getfattr --absolute-names "$@" |& _filter_test_dir
 }
 
 setfattr()