generate-inventory: do not consider nodes_roles as the source of truth

The changes made in ac95306 have been observed to cause unintended
behaviours when not all nodes are specified explicitly in PDF/IDF.
Since the original intent of the change was simply to allow running
workloads on master nodes, reverting most of that change and simply
adding the required change for master nodes. Keeping the definitions
of nodemap and rolemap as they may prove useful in future.

Signed-off-by: Cian Johnston <cian.johnston@est.tech>
Change-Id: I67bcdd9acd09261c2c5a1f7f4320ba7cdeaebaee
1 file changed