This allows to manage groups of VMs across multiple infrastructure
providers. It also adds support to create groups of VMs on OpenStack.
WARNING: the syntax of workshopctl has changed slightly. Check READMEs
for details.
`trap ... ERR` does not automatically propagate to functions. Therefore,
Our fancy error-reporting mechanism did not catch errors happening in
functions; and we do most of the actual work in functions. The solution
is to `set -E` or `set -o errtrace`.
