* 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
Don't use depth: 1 or ignore_errors in git tasks.
Commit history is nice, and since you can't do most things without the
repositories, we should fail closed upon errors.
Creates variable for 'gitian_builder_url', so we can switch out @ageis's fork
with the official @devrandom repo once a pending pull request is merged.
Changes default zcash_version to 'master' in defaults/main.yml.