Merge #12284: Remove assigned but never used local variables. Enable Travis checking for unused local variables.

ea04bf7862 Enable flake8 warning F841 ("local variable 'foo' is assigned to but never used") (practicalswift)
169f3e8637 Remove assigned but never used local variables (practicalswift)

Pull request description:

  Remove assigned but never used local variables. Enable Travis checking for unused local variables.

Tree-SHA512: d6052ec9044c5d1f03d874ea3c8addd5a156779213ef9200f89d3ae53230f2fd1691aff405c3dae14178e5ef09912c4432e92f606ef4a5220ed9daa140cdee81

test/functional/test_framework/authproxy.py

@@ -151,7 +151,7 @@ class AuthServiceProxy():
         req_start_time = time.time()
         try:
             http_response = self.__conn.getresponse()
-        except socket.timeout as e:
+        except socket.timeout:
             raise JSONRPCException({
                 'code': -344,
                 'message': '%r RPC took longer than %f seconds. Consider '

test/functional/test_framework/blockstore.py

@@ -87,7 +87,7 @@ class BlockStore():
         block.calc_sha256()
         try:
             self.blockDB[repr(block.sha256)] = bytes(block.serialize())
-        except TypeError as e:
+        except TypeError:
             logger.exception("Unexpected error")
         self.currentBlock = block.sha256
         self.headers_map[block.sha256] = CBlockHeader(block)
@@ -147,7 +147,7 @@ class TxStore():
         tx.calc_sha256()
         try:
             self.txDB[repr(tx.sha256)] = bytes(tx.serialize())
-        except TypeError as e:
+        except TypeError:
             logger.exception("Unexpected error")
 
     def get_transactions(self, inv):