test: remove invalid part of stream2-stderr-sync

One test case in test-stream2-stderr-sync.js was creating a TTY
object using an undocumented constructor and passing in fd 2.
However, this is running in a child process and fd 2 is actually
a pipe, not a TTY.

The constructor fails on Windows and causes the handle type to be
left uninitialized, which later causes an assert to fail.

On Unix, the constructor fails to retrieve the windows size but unlike
on Windows, it just leaves the size fields undefined and continues
with initializing the stream type, yielding a semi-usable object.

I could make the Windows version match Unix behavior, but it
seems to me that the test is relying on an implementation detail of
an undocumented API, and the Unix behavior is not necessarily more
correct than the Windows one. Thus it makes more sense to remove this
test.
src: make stdout/sterr pipes blocking

Expose `setBlocking` on Pipe's and if a pipe is being created for stdio
on windows then make the pipes blocking.

This fixes test-stream2-stderr-sync.js on Windows.

Fixes #3584
test: fix async-listener-run-error-once

Rely on defined order of operations by closing the server and
destorying the client socket, instead of when setImmediate fires
test: add failing http `agent: null` test

See #7012.
http, https: don't depend on `globalAgent`

For the `request()` and `get()` functions. I could never
really understand why these two functions go through agent
first... Especially since the user could be passing `agent: false`
or a different Agent instance completely, in which `globalAgent`
will be completely bypassed.

Moved the relevant logic from `Agent#request()` into the
`ClientRequest` constructor.

Incidentally, this commit fixes #7012 (which was the original
intent of this commit).
test: update "http-*" tests to only use public API

Don't invoke the `agent.requst()` or `agent.get()` functions
directly. Instead, use the public API and pass the agent
instance in as the `agent` option.
http: remove the circular dependency

Between `ClientRequest` and `Agent`. The circular require was doing
weird things at load time, like making the `globalAgent` property
be `undefined` from within the context of the "_http_client"
module.

Removing the circular dependency completely fixes this.

This commit effectively removes the undocumented `Agent#request()`
and `Agent#get()` functions.
uv: Upgrade to v0.11.21
src: update to latest libuv api

libuv gyp builds now require you to define the library disposition
(static or shared).

Also, libuv now supports vectored IO for file system reads and writes,
update to those function signatures
src: spawn_sync should close handles upon exit

When the exit callback is fired for the child process we should close
the handle associated with it.