qemu-capabilities: Fix query-cpu-model-expansion on s390 with older kernel

qemu-capabilities: Fix query-cpu-model-expansion on s390 with older kernel

When running on s390 with a kernel that does not support cpu model checking and
with a Qemu new enough to support query-cpu-model-expansion, the gathering of qemu
capabilities will fail. Qemu responds to the query-cpu-model-expansion qmp
command with an error because the needed kernel ioct does not exist. When this
happens a guest cannot even be defined due to missing qemu capabilities data.

This patch fixes the problem by silently ignoring generic errors stemming from
calls to query-cpu-model-expansion.

Reported-by: Farhan Ali <alifm@linux.vnet.ibm.com>
Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>