[ISSUE #481]Fixed the issue that reset location cannot be consumed immediately

[humkum]

fix #481

Root cause of the problem：

1. The consumer would set all exist pull request as dropped and do rebalance after change the local offset and the broker's consumption offset.
   
2. But the pull request was not removed from the cache in RebalanceImp.cpp
3. When doRebalance immediately after reset offset success, the new pull request can not assign to target message queues, which should be consumed by the client.

[humkum]

@ShannonDing @ifplusor Could you please help to review this pr?