Provide binary upgrade mechanism

[dasanchez]

In order to upgrade the binary, we need to set/change several variables in the inventory file.
Using a local testnet that uses cosmovisor as an example (the fix from issue #133 must be in place for this to work):

Starting inventory file

gaiad_version: v6.0.4
gaiad_create_validator: true
gaiad_home_autoclear: true
gaiad_unsafe_reset: true

Upgrade inventory file

gaiad_version: v7.0.2
gaiad_create_validator: false
gaiad_home_autoclear: false
gaiad_unsafe_reset: false

We could have a cleaner way to tell the playbook "I want to upgrade to version x".