Add refactored auth tests

[padelsbach]

Notes:

• When auth is enabled, the posix test now logs in as admin before any tests run so the server allows all messages (see preexisting if (server->auth != NULL) check in
  wh_Server_HandleRequestMessage)
• Auth tests mostly copied verbatim, except:
  • no separate setup/teardown of server in each test, and instead:
  • at start of each auth test, logout to establish baseline
  • at end of each auth test, log out of any test users, and re-login as admin
• Fix in legacy code: free testuser4 which was silently leaked

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #398

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