[micro_ai] tag setup functions: clean up to eliminate lots of duplicate code

As a side effect, key ca_id= is now an optional parameter for all MAIs.
 It did not make sense to disentangle this into a separate commit.
Recruiting Micro AIs: rename variables

This is necessary because there is now no distinction between
parameters passed as keys or tags in the [micro_ai] tag setup functions
for all MAIs.  No change in functionality.