box: test the assertion failure after a spurious wakeup in promote

The failure itself was fixed in 68de875
(raft: replace raft_start_candidate with _promote), let's add a
regression test now.

Follow-up #3055

test/replication/gh-3055-promote-wakeup-crash.result

@@ -0,0 +1,48 @@
+-- test-run result file version 2
+test_run = require('test_run').new()
+ | ---
+ | ...
+--
+-- gh-3055 follow-up: box.ctl.promote() could crash on an assertion after a
+-- spurious wakeup.
+--
+_ = box.space._cluster:insert{2, require('uuid').str()}
+ | ---
+ | ...
+box.cfg{election_mode='manual',\
+        replication_synchro_quorum=2,\
+        election_timeout=1000}
+ | ---
+ | ...
+
+fiber = require('fiber')
+ | ---
+ | ...
+f = fiber.create(function() box.ctl.promote() end)
+ | ---
+ | ...
+f:set_joinable(true)
+ | ---
+ | ...
+f:wakeup()
+ | ---
+ | ...
+fiber.yield()
+ | ---
+ | ...
+
+-- Cleanup.
+f:cancel()
+ | ---
+ | ...
+f:join()
+ | ---
+ | - false
+ | - fiber is cancelled
+ | ...
+box.cfg{election_mode='off'}
+ | ---
+ | ...
+test_run:cleanup_cluster()
+ | ---
+ | ...

test/replication/gh-3055-promote-wakeup-crash.test.lua

@@ -0,0 +1,21 @@
+test_run = require('test_run').new()
+--
+-- gh-3055 follow-up: box.ctl.promote() could crash on an assertion after a
+-- spurious wakeup.
+--
+_ = box.space._cluster:insert{2, require('uuid').str()}
+box.cfg{election_mode='manual',\
+        replication_synchro_quorum=2,\
+        election_timeout=1000}
+
+fiber = require('fiber')
+f = fiber.create(function() box.ctl.promote() end)
+f:set_joinable(true)
+f:wakeup()
+fiber.yield()
+
+-- Cleanup.
+f:cancel()
+f:join()
+box.cfg{election_mode='off'}
+test_run:cleanup_cluster()

test/replication/suite.cfg

@@ -3,6 +3,7 @@
     "anon_register_gap.test.lua": {},
     "gh-2991-misc-asserts-on-update.test.lua": {},
     "gh-3055-election-promote.test.lua": {},
+    "gh-3055-promote-wakeup-crash.test.lua": {},
     "gh-3111-misc-rebootstrap-from-ro-master.test.lua": {},
     "gh-3160-misc-heartbeats-on-master-changes.test.lua": {},
     "gh-3247-misc-iproto-sequence-value-not-replicated.test.lua": {},