session02: hard-code the value of the macro CLONE_STACK_SIZE

The macro PAGE_SIZE is declared in the following way in Debian:

 #define PAGE_SIZE               (sysconf(_SC_PAGESIZE))

that makes it impossible to use the macro as the size of
the array clone_args::stack since this generates the following error:

cc -g -O2 -Wall -Werror -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=0 -iquote ../../lib/arch/arm/include -I../../lib   session02.c ../../lib/libzdtmtst.a   -o session02
session02.c:70:7: error: variably modified 'stack' at file scope

Cc: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm/live/static/session02.c

@@ -64,7 +64,7 @@ static void mainloop()
 		handle_command();
 }
 
-#define CLONE_STACK_SIZE	PAGE_SIZE
+#define CLONE_STACK_SIZE	4096
 /* All arguments should be above stack, because it grows down */
 struct clone_args {
 	char stack[CLONE_STACK_SIZE];