Disable nested-virt-centos-8 from vexxhost-ca-ymq-1

A bug in the Linux kernel impacting AMD-based KVM bare metal hosts
crashes CentOS 8 nested guests. This bug is hitting provider
vexxhost-ca-ymq-1 (AMD EPYC CPUs), while it is not observed in other
nodepool providers (Intel CPUs).

We suspect this bug [1] has been fixed in kernel master [2] and in
stable versions.

Temporarily disable nested-virt-centos-8 from vexxhost-ca-ymq-1 until
the kernel is updated on the impacted bare metal hosts.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=206877
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=841c2be09fe4f495fe5224952a419bd8c7e5b455

Change-Id: I8c03d6ae687a8c3003015a4e6d7351ff81cedad2

nodepool/nl03.openstack.org.yaml

@@ -236,11 +236,6 @@ providers:
             flavor-name: 'osf-highcpu-8'
             diskimage: centos-7
             key-name: infra-root-keys-2020-05-13
-          - name: nested-virt-centos-8
-            min-ram: 8000
-            flavor-name: 'osf-highcpu-8'
-            diskimage: centos-8
-            key-name: infra-root-keys-2020-05-13
       - name: vexxhost-specific
         max-servers: 20
         labels: