libvirt: convert cpu features attribute from list to a set

Currently, the cpu features list which is being sent to libvirt,
when creating a domain or calling compareCPU, must contain only
unique entries. Multiple issues arise when we are updating the
features attribute in LibvirtConfigCPU class (for example during
migration).

This change will change the features attribute from being a list
to a set. This make the LibvirtConfigCPU class keep only unique
features.
Adjusting the LibvirtConfigCPUFeature class to support set
operations by overriding the __eq__, __ne__ and __hash__
methods.

Closes-Bug: #1303536
Change-Id: I6350fe0e827c860aea77cc4fe56f18f5c1483580
Cherry-pick-x: 60c899b9da8d64b4a5979b69c43c77ed9d5bf248
Fixes Hyper-V SCSI slot selection

Currently, when attaching volumes, the Hyper-V driver selects the
slot on the SCSI controller by using the number of drives
attached to that controller.

This leads to exceptions when detaching volumes having lower
numbered slots and then attaching a new volume, as Hyper-V will
then try to use an occupied slot.

This patch fixes the issue by simply getting a list of used slots
and getting a slot that it's not among those. It also checks
for the slot number to be smaller than the maximum number of slots
per SCSI controller.

Fixes bug: #1329764

(cherry-picked from commit a73e31022c9fef532cc2d66462d13f4ab2358565)

Change-Id: Id0c09c4debc848004a78971670cc3caef2f77ce3
Merge "Fixes Hyper-V SCSI slot selection" into stable/icehouse
Merge "libvirt: convert cpu features attribute from list to a set" into stable/icehouse
Merge remote-tracking branch 'upstream/stable/icehouse' into stable/icehouse