test plugins/coin_moves: clean up/tidy coin moves plugin logic

removes unused in-memory stash of coin-moves; don't write the entire set
of coinmoves out on every update.

tests/plugins/coin_movements.py

@@ -9,36 +9,23 @@ import os.path
 plugin = Plugin()
 
 
-@plugin.init()
-def init(configuration, options, plugin):
-    if os.path.exists('moves.json'):
-        jd = {}
-        with open('moves.json', 'r') as f:
-            jd = f.read()
-        plugin.coin_moves = json.loads(jd)
-    else:
-        plugin.coin_moves = []
-
-
 @plugin.subscribe("coin_movement")
 def notify_coin_movement(plugin, coin_movement, **kwargs):
     plugin.log("coin movement: {}".format(coin_movement))
-    plugin.coin_moves.append(coin_movement)
 
     # we save to disk so that we don't get borked if the node restarts
     # assumes notification calls are synchronous (not thread safe)
-    with open('moves.json', 'w') as f:
+    with open('moves.json', 'a') as f:
-        f.write(json.dumps(plugin.coin_moves))
+        f.write(json.dumps(coin_movement) + ',')
 
 
 @plugin.method('listcoinmoves_plugin')
 def return_moves(plugin):
     result = []
     if os.path.exists('moves.json'):
-        jd = {}
         with open('moves.json', 'r') as f:
             jd = f.read()
-        result = json.loads(jd)
+        result = json.loads('[' + jd[:-1] + ']')
     return {'coin_moves': result}