labs: option to set number of vCPUs for each node

Currently, all nodes get the default number of vCPUs (1). With this
patch, the number of vCPUs can be set in a node's configuration
file.

For the compute node, we set the number of vCPUs to 2.

Change-Id: I137be612bc6cb8f2d31adfd756404a9c6349e3c5
Implements: blueprint openstack-training-labs
Merge "labs: option to set number of vCPUs for each node"