Add missing get_available_nodes() refresh arg

In commit 3d96f85 (review I22c8d70e3e70f2d2421915da66c2618688e0db2b)
we added a refresh=False kwarg to get_available_nodes() but forgot to
add the arg to the baremetal and vmware drivers.

Use the kwarg in tests to catch this case.

Change-Id: Ib7998aafefdeac47bfad53614927c0346f193adf
Merge "Add missing get_available_nodes() refresh arg"