The genesis blocks are not really part of the wire protocol rather they
are part of a network parameters. Thus, this commit moves the all of the
gensis blocks and tests to the btcnet package.
Also, create variables in the test package for the mainnet genesis hash,
merkle root, and coinbase transaction for use throughout the tests since
they the exported values are no longer available.
This commit corrects the MsgGetBlocks tests so that the protocol version
in the multiLocators data matches the wire encoded test data. This will
help future proof the tests against protocol changes. Also, while here
modify the casing of the local vars to be consistent.
