[Test] Extended test coverage for chain reorg during superblock and payments order.

[furszy]

Built on top of #2427..
Expanded unit test coverage for the blockchain reorg during superblock range (parallel work of #2436), budget proposal payments distribution in different order and the creation of an invalid budget finalization.

[random-zebra]

Looks good. tiertwo_governance_invalid_budget.py could use some more cleanup (removing the unused node minerB, leftover from tiertwo_reorg_mempool.py):

Index: test/functional/tiertwo_governance_invalid_budget.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/test/functional/tiertwo_governance_invalid_budget.py b/test/functional/tiertwo_governance_invalid_budget.py
--- a/test/functional/tiertwo_governance_invalid_budget.py	(revision 0961e50fd575ec00950e2925d4be77a6c144e0bb)
+++ b/test/functional/tiertwo_governance_invalid_budget.py	(date 1626277927433)
@@ -16,19 +16,17 @@
 
     def set_test_params(self):
         self.setup_clean_chain = True
-        # 4 nodes:
+        # 3 nodes:
         # - 1 miner/mncontroller
         # - 2 remote mns
-        # - 1 other node to stake a forked chain
-        self.num_nodes = 4
+        self.num_nodes = 3
         self.extra_args = [["-sporkkey=932HEevBSujW2ud7RfB1YF91AFygbBRQj3de3LyaCRqNzKKgWXi"],
                            [],
-                           ["-listen", "-externalip=127.0.0.1"],
-                           ["-listen", "-externalip=127.0.0.1"],
+                           [],
                            ]
         self.enable_mocktime()
 
-        self.minerAPos = 0
+        self.minerPos = 0
         self.remoteOnePos = 1
         self.remoteTwoPos = 2
 
@@ -39,27 +37,27 @@
         self.mnTwoPrivkey = "92Hkebp3RHdDidGZ7ARgS4orxJAGyFUPDXNqtsYsiwho1HGVRbF"
 
     def run_test(self):
-        self.minerA = self.nodes[self.minerAPos]     # also controller of mn1 and mn2
+        self.miner = self.nodes[self.minerPos]     # also controller of mn1 and mn2
         self.mn1 = self.nodes[self.remoteOnePos]
         self.mn2 = self.nodes[self.remoteTwoPos]
         self.setupContext()
 [...]

[furszy]

Done, squashed it inside the last commit.

[random-zebra]

utACK 6805ee8