Summary:
Fix unstable floating point exception, tested on Windows, 64-bit build.
The problem appeared in `SetCapacity()` method at line
`high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;`
`high_pri_pool_ratio_` was not initialized at that moment, because
`SetHighPriorityPoolRatio()` is called after `SetCapacity()`. So,
`high_pri_pool_ratio_` contained garbage, which caused "Floating point
exception" sometimes.
Closes https://github.com/facebook/rocksdb/pull/3052
Differential Revision: D6111161
Pulled By: yiwu-arbug
fbshipit-source-id: d170329111ad12b4bf9bbcf37bcb6411523438ae
ee2b1ec1e8