+++ This bug was initially created as a clone of Bug #1576799 +++

Backport the following commit to RHOS-12:

commit facde6cad8bc7ce0fd4d251f86550a7f648a5a13
Author: Kashyap Chamarthy <kchamart>
Date:   Sat Apr 28 18:55:25 2018 +0200

    libvirt: Make `cpu_model_extra_flags` case-insensitive for real
    
    When we introduced `cpu_model_extra_flags` config attribute (in
    commit: 6b601b7 -- "libvirt: Allow to specify granular CPU feature
    flags"), we said it was case-insensitive; but unfortunately I missed to
    _really_ make it so (despite proposing code for it in one of the
    revisions).
    
    Address that mistake by making `cpu_model_extra_flags` case-insensitive
    for real, from Nova's point of view.
    
    NB: Internally, this patch is normalizing 'extra_flags' to _lower_
    casing -- because CPU flags _must_ be lower case from libvirt's point of
    view.  Nova must honour that; otherwise, launching instances with an
    upper case CPU flag, 'FOO', will fail with: "libvirtError: internal
    error: Unknown CPU feature FOO".
    
    Upstream-Queens: https://review.openstack.org/565668
    Related-Bug: #1750829
    Change-Id: Ia7ff0566a5109c76c009f3a0c6199c4ba419cfb1
    Reported-by: Daniel P. Berrangé <berrange>
    Signed-off-by: Kashyap Chamarthy <kchamart>