Correct intent of function names in nodes

_create_or_register_{bm,ironic}_node does not express the intent
of the function, since creating a node is the same as registering it.
Fix this thinko by calling the functions
_update_or_register_{bm,ironic}_node.

Change-Id: Ifa5932b78a103655885af3742eeda8156b457822
Merge "Correct intent of function names in nodes"