libvirt: test setting of CPU tuning data

The setting of the libvirt guest <cputune> data from the
flavor extra_specs quota parameter was never tested. In
fixing this omission, it was noticed that the data was
incorrectly passed around as a string instead of an int.

Change-Id: Ie8b31feddf6c546eb05ca00ead5c56bcd535dd84
VMware: validate that VM exists on backend prior to deletion

Attempting to delete an instance that does not exist on the backend
throws an exception (for example UnregisterVM may return this when
running the CI).

Change-Id: I1b95caec2dad6580db576aa6f80f47913b7c066e
Closes-bug: #1300788
libvirt: Add configuration of guest VCPU topology

Wire up the libvirt driver to honour the VCPU topology config
requested via the flavor extra specs / image meta. This is
only done for QEMU/KVM guests at this time. Although Xen is
technically capable of supporting this, it is not yet wired
up in libvirt itself.

Blueprint: virt-driver-vcpu-topology
Change-Id: I4540147af7b91e1dc463be63d19afbfcfc1216cb
Merge "libvirt: test setting of CPU tuning data"
Merge "libvirt: Add configuration of guest VCPU topology"
Merge "VMware: validate that VM exists on backend prior to deletion"