Due to the way we're now calculating delegate_to, if that value is based
on a loop variable ('item') we need to calculate all of the possible
delegated_to variables for that loop.
Fixes#12499
* Speed up serialization of hostvars by simply using the internal
dictionary used for cached lookups
* Use blocking gets/puts on queues instead of spin locking
* Merge sequential implicitly created blocks
Also making PlayContext a child class of the Playbook Base class,
which gives it access to all of the FieldAttribute code to ensure
field values are correctly typed after post_validation
Fixes#11381
* PluginLoader class will now be more selective about loading some
plugin classes, if a required base class is specified (used to avoid
loading v1 plugins that have changed significantly in their apis)
* Added ability for the connection info class to read values from a
given hosts variables, to support "magic" variables
* Added some more magic variables to the VariableManager output
* Fixed a bug in the ActionBase class, where the module configuration
code was not correctly handling unicode
James Cammarata
Toshio Kuratomi
Marius Gedminas