test-tool: add LogoutDuringIOAsync test case

This attempts to reproduce upstream LIO reports of a use after free bug
when logout occurs alongside concurrent I/O.

Signed-off-by: David Disseldorp <ddiss@suse.de>

test-tool/iscsi-test-cu.h

@@ -258,6 +258,7 @@ void test_write10_wrprotect(void);
 void test_write10_dpofua(void);
 void test_write10_residuals(void);
 void test_async_write(void);
+void test_async_io_logout(void);
 
 void test_write12_simple(void);
 void test_write12_beyond_eol(void);