test-tool: add PrinReadKeys.Truncate test

This test registers PR key and then sends a PR-In read-keys request with
an ALLOCATION LENGTH value that forces response truncation. Ensure that
the ADDITIONAL LENGTH is *not* modified as a result of the truncation.

This test currently passes against TGT but fails against LIO (fix
pending).

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

test-tool/iscsi-test-cu.h

@@ -115,6 +115,7 @@ void test_preventallow_lun_reset(void);
 void test_preventallow_2_itnexuses(void);
 
 void test_prin_read_keys_simple(void);
+void test_prin_read_keys_truncate(void);
 void test_prin_serviceaction_range(void);
 void test_prin_report_caps_simple(void);