Improvements to s2nc/s2nd/echo

[maddeleine]

Security issue notifications

If you discover a potential security issue in s2n we ask that you notify
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Problem:

Our test server and client have some "funky" behavior. We should make them easier to understand and use.

Solution:

• A user should be able to input how many reconnects they want with the -r flag, rather than s2nc using an arbitrary constant.
• Is the early_data_recv function printing out an extra new line? Investigate and fix.
• The echo function is complex and unreadable. We should get rid of the nested while loops if possible 👀
• The session ticket reconnect behavior in TLS1.2 re-uses the same session ticket 5 of times. We probably want a new session ticket for each reconnect.

• Does this change what S2N sends over the wire? No
• Does this change any public APIs? No
• Which versions of TLS will this impact?
  None

Requirements / Acceptance Criteria:

Fix all the above issues.

• RFC links: N/A
• Related Issues: N/A
• Will the Usage Guide or other documentation need to be updated? No
• Testing: All current integ tests pass
  • Will this change trigger SAW changes? No
  • Should this change be fuzz tested? No

Out of scope:

N/A