Feature: add retry to net fetcher

Due to the quality of the network, I often encounter similar problems:

Verification for unzip failed due to a checksum mismatch:
    expected: 036d96991646d0449ed0aa952e4fbe21b476ce994abc276e49d30e686708bd37
    actual:   bb6f1d15b04e1bb4b27eff4620b647ea6f06bea4dba8bef5eea9c3e4ce96fff6

Instability of the network leads to incomplete downloaded resources.

checksum mismatch will cause the entire rake build:project to fail, usually retrying will solve the problem.