tests: re-organize and enable xref and coverage
start.sh: pass in cli args
WIP
test: use the "test" hypervisor driver

Switch to using the libvirt test driver. This has some issues:

* automatically creates the domain (do not need to call
  verx:define_domain_xml/2 and verx:domain_create/2)

* does not support the full set of commands, e.g.,
  verx:node_get_free_memory/2)

* doesn't create a virtual machine

Testing all of the permutations of transports/hypervisors is difficult,
since the hypervisor support varies.
tests: remove KVM and LXC tests

Simplify the tests by removing support for KVM and LXC.