Fix crash caused by receiving `#append_entries_reply{success=false}` from unknown peer

[sile]

Proposed Changes

This PR fixes a ra server process (leader) crash caused by receiving a #append_entries_reply{success=false} message from an unknown peer.

Types of Changes

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• [x] Bug fix (non-breaking change which fixes issue #NNNN)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation (correction or otherwise)
• [ ] Cosmetics (whitespace, appearance)

Checklist

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• [x] I have read the CONTRIBUTING.md document
• [x] I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• [x] All tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)
• [ ] Any dependent changes have been merged and published in related repositories

Further Comments

If the patch in this PR is not applied, the following crash log will be generated by the append_entries_reply_no_success_from_unknown_peer test case.

=== Location: [{ra_server,handle_leader,472},
              {ra_server_SUITE,append_entries_reply_no_success_from_unknown_peer,989},
              {test_server,ts_tc,1794},
              {test_server,run_test_case_eval1,1303},
              {test_server,run_test_case_eval,1235}]
=== === Reason: no match of right hand side value 
                 #{{n1,'ct_ra@localhost'} =>
                       #{status => normal,next_index => 1,match_index => 0,
                         query_index => 0,commit_index_sent => 0}}
  in function  ra_server:handle_leader/2 (src/ra_server.erl, line 472)
  in call from ra_server_SUITE:append_entries_reply_no_success_from_unknown_peer/1 (test/ra_server_SUITE.erl, line 989)
  in call from test_server:ts_tc/3 (test_server.erl, line 1794)
  in call from test_server:run_test_case_eval1/6 (test_server.erl, line 1303)
  in call from test_server:run_test_case_eval/9 (test_server.erl, line 1235)

[kjnilsson]

thank you @sile !

[sile]

👍