[REEF-1571] Switch to AppVeyor DownloadFile command
[REEF-1571] Switch to AppVeyor DownloadFile command

This change switches from Start-FileDownload cmdlet
to AppVeyor DownloadFile command in our AppVeyor install
dependencies script.

JIRA:
  [REEF-1571](https://issues.apache.org/jira/browse/REEF-1571)

Pull request:
  This closes #1128

jwang98052/incubator-reef,singlis/reef,motus/reef,markusweimer/incubator-reef,singlis/reef,tcNickolas/incubator-reef,dongjoon-hyun/reef,jwang98052/reef,singlis/reef,dongjoon-hyun/reef,dougmsft/reef,shravanmn/reef,singlis/reef,anupam128/reef,tcNickolas/incubator-reef,dougmsft/reef,apache/reef,dongjoon-hyun/incubator-reef,apache/incubator-reef,tcNickolas/reef,apache/incubator-reef,markusweimer/reef,anupam128/reef,jwang98052/incubator-reef,anupam128/reef,markusweimer/incubator-reef,nachocano/incubator-reef,dougmsft/reef,jwang98052/reef,jwang98052/incubator-reef,shravanmn/reef,singlis/reef,anupam128/reef,dongjoon-hyun/incubator-reef,apache/reef,dongjoon-hyun/reef,dougmsft/reef,markusweimer/reef,tcNickolas/incubator-reef,afchung/incubator-reef,tcNickolas/reef,jwang98052/reef,jwang98052/reef,dongjoon-hyun/incubator-reef,jwang98052/incubator-reef,tcNickolas/reef,afchung/reef,afchung/incubator-reef,afchung/reef,apache/reef,shravanmn/reef,afchung/reef,afchung/incubator-reef,markusweimer/reef,dongjoon-hyun/reef,singlis/reef,apache/incubator-reef,markusweimer/incubator-reef,tcNickolas/incubator-reef,shravanmn/reef,dongjoon-hyun/incubator-reef,markusweimer/reef,jwang98052/reef,dongjoon-hyun/incubator-reef,tcNickolas/incubator-reef,tcNickolas/reef,jwang98052/incubator-reef,apache/reef,nachocano/incubator-reef,afchung/reef,apache/incubator-reef,dongjoon-hyun/reef,jwang98052/reef,apache/reef,dongjoon-hyun/incubator-reef,apache/reef,tcNickolas/reef,shravanmn/reef,jwang98052/incubator-reef,dongjoon-hyun/reef,motus/reef,tcNickolas/incubator-reef,motus/reef,shravanmn/reef,nachocano/incubator-reef,markusweimer/incubator-reef,markusweimer/incubator-reef,apache/reef,motus/reef,apache/incubator-reef,tcNickolas/incubator-reef,afchung/incubator-reef,motus/reef,afchung/reef,anupam128/reef,dougmsft/reef,nachocano/incubator-reef,afchung/incubator-reef,anupam128/reef,markusweimer/incubator-reef,tcNickolas/reef,tcNickolas/reef,nachocano/incubator-reef,dougmsft/reef,afchung/reef,anupam128/reef,nachocano/incubator-reef,markusweimer/reef,markusweimer/reef,markusweimer/incubator-reef,jwang98052/incubator-reef,dongjoon-hyun/reef,motus/reef,dongjoon-hyun/incubator-reef,nachocano/incubator-reef,dougmsft/reef,apache/incubator-reef,singlis/reef,markusweimer/reef,jwang98052/reef,shravanmn/reef,afchung/incubator-reef,afchung/incubator-reef,apache/incubator-reef,afchung/reef,motus/reef