Replace ReconsiderProxyAfterError tests

JobControllerReconsiderProxyAfterErrorTest.ReconsiderProxyAfterError
made TCP reads return errors that normally can't be returned from TCP
reads, resulting in an overly synthetic test that could hide real
issues (e.g., some errors it was returning from the TCP layer are
typically mapped to other errors that can be returned by higher layers,
which is what the proxy code actually sees).

This CL reworks the test to return errors (mostly) from the correct
layers.

It also adds HTTP and SOCKS5 proxy tests.

This also fixes a bug where the test was intended to create two
connections, but the second attempt to create a connection was actually
pulling the idle connection from the first connection attempt out of
the socket pool.

Bug: 1286386
Change-Id: Iffa729cc062634115f3f97033f06304260a98bf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3380011
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#957877}