refresh whitelist based on wallet health (fixes #60)

Refreshs the whitelist in each iteration based on the wallet health,
disabled wallets will be removed from the whitelist automatically.

freqtrade/tests/conftest.py

@@ -37,7 +37,8 @@ def default_conf():
                 "BTC_ETH",
                 "BTC_TKN",
                 "BTC_TRST",
-                "BTC_SWT"
+                "BTC_SWT",
+                "BTC_BCC"
             ]
         },
         "telegram": {
@@ -90,6 +91,36 @@ def ticker():
     })
 
 
+@pytest.fixture
+def health():
+    return MagicMock(return_value=[{
+        'Currency': 'BTC',
+        'IsActive': True,
+        'LastChecked': '2017-11-13T20:15:00.00',
+        'Notice': None
+    }, {
+        'Currency': 'ETH',
+        'IsActive': True,
+        'LastChecked': '2017-11-13T20:15:00.00',
+        'Notice': None
+    }, {
+        'Currency': 'TRST',
+        'IsActive': True,
+        'LastChecked': '2017-11-13T20:15:00.00',
+        'Notice': None
+    }, {
+        'Currency': 'SWT',
+        'IsActive': True,
+        'LastChecked': '2017-11-13T20:15:00.00',
+        'Notice': None
+    }, {
+        'Currency': 'BCC',
+        'IsActive': False,
+        'LastChecked': '2017-11-13T20:15:00.00',
+        'Notice': None
+    }])
+
+
 @pytest.fixture
 def limit_buy_order():
     return {