[gitian] use versioned unsigned tarballs instead of generically named ones
[gitian] use versioned unsigned tarballs instead of generically named ones

Instead of re-naming the tarballs used for the code signing step to the generically
named tarball that is used, keep the versioned naming. Only copy them to the
correct filename when they are needed at build time.

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin