aio-dio-regress: align I/O buffers to 4k for 4k sector devices

(and virtual devices as found on s390)

Without this patch, these tests can randomly fail on s390 systems which
use a virtual block device with sector size of 4k.  Testing confirms
that this patch resolves the issue.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>

src/aio-dio-regress/aio-dio-extend-stat.c

@@ -46,7 +46,7 @@
 
 #define BUFSIZE 1024
 
-static unsigned char buf[BUFSIZE] __attribute((aligned (512)));
+static unsigned char buf[BUFSIZE] __attribute((aligned (4096)));
 
 /* 
  * this was arbitrarily chosen to take about two seconds on a dual athlon in a

src/aio-dio-regress/aio-dio-invalidate-failure.c

@@ -54,7 +54,7 @@
 /* This test never survived to 180 seconds on a single spindle */
 #define SECONDS 200
 
-static unsigned char buf[GINORMOUS] __attribute((aligned (512)));
+static unsigned char buf[GINORMOUS] __attribute((aligned (4096)));
 
 #define fail(fmt , args...) do {\
 	printf(fmt , ##args);	\

src/aio-dio-regress/aio-dio-subblock-eof-read.c

@@ -49,7 +49,7 @@ do {				\
 	exit(1);		\
 } while (0)
 
-static unsigned char buffer[4096] __attribute((aligned (512)));
+static unsigned char buffer[4096] __attribute((aligned (4096)));
 
 int
 main(int argc, char **argv)