Integrate multinode tests into Drone CI

the following process is suggested:

• after building and publishing server and columnstore packages Drone call scripts on the host to create virtual machines and setup cluster
• script on the host provides credentials to access the primary node
• MTR can be executed in the container or on one of the virtual machines (primary?)
• logs have to be copied from all virtual machines
• VMs have to be deleted: it should be "always executed step" + MDBCI cloud monitor will report all old VMs (and possibly destroy them automatically after a certain time)
• scripts can be executed manually from the host

Communication between container and the Drone host:

• curl: the server has to be created on the host, and access to the server has to be restricted
• ssh: only private key is needed on the container side

To be implemented:

• MDBCI should support Drone CI repos https://cspkg.s3.amazonaws.com/index.html
• (probable) script to run MTR from the host on the one of VMs (to make running MTR without Drone easier)

the first implementation of the scripts to create VMs and cluster https://github.com/mariadb-corporation/mariadb-columnstore-engine/tree/TODO-4505-multinode-scripts/tests/mdbci