Build release candidates

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Evo masternodes are set up using mn-bootstrap to enable easier deploy of platform services. In order to be able to properly test deploying with this tool on evonet and testnet, it would be great to have access to release candidate builds from Docker Hub by specifying a tag, i.e. here: https://hub.docker.com/repository/docker/dashpay/dashd

There is also an option to use https://hub.docker.com/repository/docker/dashpay/dashd-develop but these images track the develop branch and may cause problems troubleshooting RC builds on testnet.