Update to use reference contracts and fix previous system contracts location error

[linh2931]

Update URL and path names to use the newly released AntelopeIO/reference-contracts.

Previously system contracts were installed in /app/eos-system-contracts but when they were deployed, they were looked in /home/www-data/eos-system-contracts. This caused the problem of system contracts not found:

dune --bootstrap-system
Preactivate Features: {"result":"ok"}
error 2022-09-09T12:45:48.788 cleos     main.cpp:4121                 operator()           ] Failed with error: 0 exception: unspecified
Unable to resolve path '/home/www-data/eos-system-contracts/build/contracts/eosio.boot'
    {"path":"/home/www-data/eos-system-contracts/build/contracts/eosio.boot","exception":"Dynamic exception type: boost::filesystem::filesystem_error\nstd::exception::what: boost::filesystem::canonical: No such file or directory: \"/home/www-data/eos-system-contracts/build/contracts/eosio.boot\"\n"}