* Add 2.0-2.3 facts api compat (ansible_facts(), get_all_facts())
These are intended to provide compatibilty for modules that
use 'ansible.module_utils.facts.ansible_facts' and
'ansible.module_utils.facts.get_all_facts' from 2.0-2.3 facts
API.
Fixes#25686
Some related changes/fixes needed to provide the compat api:
* rm ansible.constants import from module_utils.facts.compat
Just use a hard coded default for gather_subset/gather_timeout
instead of trying to load it from non existent config if the
module params dont include it.
* include 'external' collectors in compat ansible_facts()
* Add facter/ohai back to the valid collector classes
facter/ohai had gotten removed from the default_collectors
class used as the default list for all_collector_classes by
setup.py and compat.py
That made gather_subset['facter'] fail.
Simon Dodsley
Brian Coca
Adrian Likins