BlockBlobService.get_blob_to_path() crashes even when if_match='*'

### Which service(blob, file, queue) does this issue concern?
BlockBlobService.get_blob_to_path()

### Which version of the SDK was used? Please provide the output of `pip freeze`.
Same issue is encountered in versions: 0.37.1, 1.3.0, and 2.1.0

**Version 0.37.1**
>pip freeze
azure-common==1.1.8
azure-nspkg==2.0.0
azure-storage==0.36.0
azure-storage-blob==0.37.1
azure-storage-common==0.37.1
azure-storage-nspkg==2.0.0

**Version 1.3.0**
>pip freeze
azure-common==1.1.8
azure-nspkg==2.0.0
azure-storage==0.36.0
azure-storage-blob==1.3.0
azure-storage-common==1.3.0
azure-storage-nspkg==2.0.0

**Latest version**
>pip freeze
azure-common==1.1.8
azure-nspkg==2.0.0
azure-storage==0.36.0
azure-storage-blob==2.1.0
azure-storage-common==2.1.0
azure-storage-nspkg==2.0.0

### What problem was encountered?
When trying to download a blob that is currently been written in append mode (i.e., the ETag changes during time of download), `BlockBlobService.get_blob_to_path()` crashes even when using `if_match='*'` giving **ConditionNotMet** Error:
`Client-Request-ID=9cce10c8-b739-11e9-9366-b32a86ae676b Retry policy did not allow for a retry: Server-Timestamp=Mon, 05 Aug 2019 04:29:28 GMT, Server-Request-ID=86bb1780-a01e-002e-6146-4b01e3000000, HTTP status code=412, Exception=The condition specified using HTTP conditional header(s) is not met. ErrorCode: ConditionNotMetConditionNotMetThe condition specified using HTTP conditional header(s) is not met.RequestId:86bb1780-a01e-002e-6146-4b01e3000000Time:2019-08-05T04:29:28.3320963Z`

### Have you found a mitigation/solution?
- Using a version before **1.3.1** and using `max_connections=1` mitigates the problem
- Downloading a very small portion of the blob (< 20 MB) will work since ETag doesn't change during time of download

Code to repro:
```
bbs = BlockBlobService(connection_string=connection_string)
bbs.get_blob_to_path(app_id, blob_name, output_fp, start_range=0, end_range=100*1024**2, if_match='*')
```

Bắt đầu tại BlockBlobService.get_blob_to_path() và chạy bản tái hiện lượt tải xuống 100 MiB được cung cấp với if_match='*' trong khi append blob đang được ghi. So sánh hành vi giữa các phiên bản SDK được liệt kê; công việc được xem là hoàn tất khi lượt tải xuống không còn bị crash với ConditionNotMet trong các điều kiện đã nêu và có coverage hồi quy cho bản tái hiện.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.