尝试使用 docker asp.net mvc5，但是卡在 dnu restore

想要将生产环境从 WINDOWS 切换到 CENTOS 来，但项目是 ASP.NET 的于是打算使用 Docker asp.net mvc5 ，参照 https://github.com/aspnet/Home/blob/dev/GettingStartedDeb.md 示例，使用 docker build -t aspnet-home-helloweb . 卡在了 dnu restore 还原包这步上，一直提示 http request timeout ，服务器是 LINODE 上的 VPS 应该不是网络环境的原因…… GOOGLE 了一下找到 https://github.com/aspnet/dnx/issues/1590 ，按里面的说法
export MONO_THREADS_PER_CPU=2000
并没有用
有人用过这个知道怎么解决吗……？

以下是 Dockerfile:

FROM microsoft/aspnet
ENV MONO_THREADS_PER_CPU = 2000
COPY project.json /app/
WORKDIR /app
RUN ["dnu", "restore", "-s", "https://api.nuget.org/v3/index.json"]
COPY . /app

EXPOSE 5004
ENTRYPOINT ["dnx", "project.json", "kestrel"]

错误提示：

Warning: FindPackagesById: System.Private.Networking
HTTP request timed out. Retrying.
GET https://az320820.vo.msecnd.net/v3-flatcontainer/system.private.networking/index.json
Warning: FindPackagesById: System.Reflection.Primitives
HTTP request timed out. Retrying.
GET https://az320820.vo.msecnd.net/v3-flatcontainer/system.reflection.primitives/index.json
Warning: FindPackagesById: System.Runtime.Handles
HTTP request timed out. Retrying.
GET https://az320820.vo.msecnd.net/v3-flatcontainer/system.runtime.handles/index.json
Error: DownloadPackageAsync: https://az320820.vo.msecnd.net/v3-flatcontainer/system.threading/4.0.10-beta-23109/system.threading.4.0.10-beta-23109.nupkg
HTTP request timed out. Exiting.
Error: DownloadPackageAsync: https://az320820.vo.msecnd.net/v3-flatcontainer/system.threading.tasks/4.0.10-beta-23109/system.threading.tasks.4.0.10-beta-23109.nupkg
HTTP request timed out. Exiting.
Error: DownloadPackageAsync: https://az320820.vo.msecnd.net/v3-flatcontainer/system.threading.thread/4.0.0-beta-23109/system.threading.thread.4.0.0-beta-23109.nupkg
HTTP request timed out. Exiting.
Error: DownloadPackageAsync: https://az320820.vo.msecnd.net/v3-flatcontainer/system.threading.threadpool/4.0.10-beta-23109/system.threading.threadpool.4.0.10-beta-23109.nupkg
HTTP request timed out. Exiting.
Error: DownloadPackageAsync: https://az320820.vo.msecnd.net/v3-flatcontainer/microsoft.aspnet.diagnostics.abstractions/1.0.0-beta6/microsoft.aspnet.diagnostics.abstractions.1.0.0-beta6.nupkg
HTTP request timed out. Exiting.