This patch fixes a number of outstanding bugs and code convention pro…

…blems. (ansible#31618)

* documentation was not inline with other Ansible modules
* Python 3 specific imports were missing
* monitor_type is no longer required when creating a new pool; it is now the default.
* A new monitor_type choice of "single" was added for a more intuitive way to specify "a single monitor". It uses "and_list" underneath, but provides additional checks to ensure that you are specifying only a single monitor.
* host and port arguments have been deprecated for now. Please use bigip_pool_member instead.
* 'partition' field was missing from documentation.
* A note that "python 2.7 or greater is required" has been added for those who were not aware that this applies for ALL F5 modules.
* Unit tests were fixed to support the above module