tests: Improve live migration tests reliability

Move the live migration tests to a 'jammy' worker rather than
'jammy-small'. This type of worker has more CPUs (64 vs 16) and more RAM
(256G vs 64G), which should improve the time it takes to run each test.
With this improvement, the test shouldn't fail anymore due to timeout
being reached.

A second improvement is to reduce the amount of vCPUs created for each
VM. The point is simply to check we can migrate a VM with multiple
vCPUs, therefore using 2 instead of 6 should be enough when possible.
When testing NUMA, we can't lower the amount of vCPUs since there's a
quite complex topology that is expected there.
Also, the total amount of vCPUs is reduced from 12 to 4 (again when not
testing with NUMA).

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

Jenkinsfile

@@ -295,7 +295,7 @@ pipeline{
 					}
 				}
 				stage ('Worker build - Live Migration') {
-					agent { node { label 'jammy-small' } }
+					agent { node { label 'jammy' } }
 					when {
 						beforeAgent true
 						expression {