* 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
Avoids a race condition where previously the registered variable message
was being sent after the 'host_task_ok' message, meaning the next task
may be started before the var is registered, leading to an undefined
variable error
* 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
