xenapi: max out VCPU count

Give as much VCPUs to the DevStack machine as possible. First asking
xenapi about its CPU count, and as a fallback, count the CPUs in dom0.
This should result in faster test runs.

Change-Id: I1ffb99ecd435f1d7eb5754fe9cd99f0e8ceae6dc
diff --git a/tools/xen/install_os_domU.sh b/tools/xen/install_os_domU.sh
index 110bbd9..e69cdea 100755
--- a/tools/xen/install_os_domU.sh
+++ b/tools/xen/install_os_domU.sh
@@ -263,6 +263,9 @@
 # Set virtual machine parameters
 set_vm_memory "$GUEST_NAME" "$OSDOMU_MEM_MB"
 
+# Max out VCPU count for better performance
+max_vcpus "$GUEST_NAME"
+
 # start the VM to run the prepare steps
 xe vm-start vm="$GUEST_NAME"