Preferring ssh-agent forwarding to copying user's ssh keys.
As a bonus, ansible tasks don't need to know or care about the name or
path of the user's ssh private key file, and the configuration is
simplified.
* Changes method for setting trust level of GPG keys
* Import keys but don't use Ansible git verify_commit
Per an upstream Ansible bug, verifying signed tags is not supported yet.
Also removes non-working scp.sh script.
Updates README to explain how to run gverify.
Changes zcash_version to v1.0.0-rc2