Expose cpu arch, number of cpus, and total memory

[PhilippMatthes]

This PR adds a capabilities client that automatically connects to libvirt and fetches capabilities of the hypervisors. The capabilities are mapped to a new v1alpha.CapabilitiesStatus struct, which is part of v1alpha.HypervisorStatus. As a starter, we export the cpu architecture, as well as the total number of cpus and memory over all numa cells.

I've also taken the freedom and removed the goconst linter. It produced two obvious false positives :)

[notandy]

works for me, although the memory looks a bit odd:

  Capabilities:
    Cpu Arch:  x86_64
    Cpus:      256
    Memory:    4227289164Ki

Which is probably ok I assume.

[PhilippMatthes]

4227289164Ki should be about right with 4 numa cells with 1056822291 KiB each.