WIP: Some patch ups for let the let the SRs can be build on a KVM with limited network accesing

1. Include the public key of Boxiang to allow Slapos to download the packages from shacache. The packages were uploaded through another KVM, which uses Boxiang's configuration.
2. Enable and customize the Goproxy, this can avoid using the default goproxy with a random IP allocated by the CDN. On the limited KVM, the specified goproxy link was pinned to a fixed IP address through the hosts file. This was done by using an ansible-playbook. (Change the default goproxy is because it using google service, I'm afraid allow it may also enable some other network accessing, so I choose a rarely used goproxy in Europe).
3. Pin the version of the PyPI packages, eg: testfixtures = 6.11.0