Fix BaseBaremetalTest._assertExpected docstring
Fix BaseBaremetalTest._assertExpected docstring

This updates the docstring for tempest plugin's
BaseBaremetalTest._assertExpected() so that it clarifies
what it is doing and what the parameters are.

Change-Id: Icd61bbbdc0f0633a93adef89652d54a87d835534

openstack/ironic,pshchelo/ironic,NaohiroTamura/ironic,SauloAislan/ironic,NaohiroTamura/ironic,openstack/ironic,pshchelo/ironic,SauloAislan/ironic