Add test for vol-download and vol-upload

```
  NAME
    vol-download - download volume contents to a file

  SYNOPSIS
    vol-download <vol> <file> [--pool <string>] [--offset <number>] [--length <number>]

  DESCRIPTION
    Download volume contents to a file

  OPTIONS
    [--vol] <string>  vol name, key or path
    [--file] <string>  file
    --pool <string>  pool name or uuid
    --offset <number>  volume offset to download from
    --length <number>  amount of data to download


  NAME
    vol-upload - upload file contents to a volume

  SYNOPSIS
    vol-upload <vol> <file> [--pool <string>] [--offset <number>] [--length <number>]

  DESCRIPTION
    Upload file contents to a volume

  OPTIONS
    [--vol] <string>  vol name, key or path
    [--file] <string>  file
    --pool <string>  pool name or uuid
    --offset <number>  volume offset to upload to
    --length <number>  amount of data to upload
```
Using md5 to verify the content 
cover 6 types of pool