Fix missing download badge. Link to shields.io.

Fixes #8261

* Better comments
* Reorganize code so related settings are close to each other
* Add ::1 to the "localhost" patterns we look for
* Make the dest_port parameter override the ansible_ssh_port setting
* Fix dest_port (wasn't being set)
* more complete detection of delegate_to
* Fix set_remote_user (wasn't being looked for in parameters)
* Instead of removing mode here, have the ansible module accept it
  (better documents the parameters doing it htat way)

So that roles are loaded ahead of all other play fields, meaning any
plugins contained within the roles are loaded first before tasks.

Fixes #11858

Fix ssh connections to IPv6 addresses

Fixes #9933

Fixes #11852

Fixes #11851

Fixes bugs related to creating Templar() objects on the fly, where
the shared loader objects (serialized to TaskExecutor) aren't used
so information loaded into plugin loaders after forking is lost.

Fixes #11815

This field is templated specially during the TaskExecutor's loop
calculation, so there's no need to post validate it again.

Fixes #11481

Add test for https://github.com/ansible/ansible/issues/9851

fixes #11808

Fixes #11836

Fixes #10858

Fixes #11839

Also modifies the Play class to not include become* fields in the
post-validation step.

Fixes #11353

And use it in the call to get the loop items for a task.

Fix for PowerShell unquote method when passed None.

Raw is not raw enough

Bug #11830, keep working even if we use private_networking

Disallow --forks 0

We can unconditionally wrap remote_addr in square brackets for scp and
sftp (both of which require them for IPv6 addresses), but not wrap them
at all for ssh (which doesn't accept them). This way, we don't have to
detect and treat IPv6 addresses specially. This works for hostnames,
IPv4 addresses, and IPv6 addresses.

The earlier code seemed to intend to wrap all IPv6 addresses in square
brackets, which would have broken ssh, but it actually made no attempt
to detect IPv6 addresses at all (so it broke only with IPv6 addresses
for scp and sftp).

Based on a review of PR #11677 by @JuiceBoxSingularity

Make 'pause: prompt=…' print the prompt

In stable-1.9, the prompt string is passed to raw_input(), which prints
it without an extra \n. Here we're just print()ing it, so the \n would
be doubled.