The ansible_processor field provides a list of all hyperthreaded cores. Using
Jinja we can just get the number of cores on the machine by running length on
this list.

Putting migratedb in group_vars/all overrides any vars
in playbook files and so migrations never get run.

In regular runs it seems to have no side effect but fails for vagrant runs.

This also makes it easier to conditionalize it since it
doesn't need to be run on workers.

For the case where  "ansible_processor_cores": "NA"  and
facter_processorcount wasn't the WORKERS was set to the string "NA" *
the multiplier (like batman).
This will try to convert both to numbers and if the conversion fails it
will fall through and just set the WORKERS to the multiplier.