tests/HttpTest: Fix build on x86_gcc2

* std::istreambuf_iterator<T> template isn't available until C++11.
* std::vector<T>::cbegin() is not available
* Add missing include of errno.h

Change-Id: Ice344f6b0f93bf72d9120674607878c4c3e8ef54
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2515
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

tests/net: HTTP proxy client test

With this patch, ProxyTest is implemented and all of the tests in
HttpTest are enabled.

Adding a transparent proxy server implementation proxy.py. Like
testserver.py, this can be provided a socket file descriptor and port
via command-line arguments.

TestServer was refactored to extract ChildProcess and
RandomTCPServerPort, which are now also used by TestProxyServer.

ProxyTest starts TestProxyServer and validates that the request is
sent to the proxy and is routed to the appropriate endpoint of the
downstream server.

The template which adds common tests between HttpTest and HttpsTest
was changed slightly to just take a BThreadedTestCaller<T>&, which
made it simpler to add additional test cases to one suite which are
not appropriate to the other. There wasn't much point in keeping that
template as a member function so I moved it into HttpTest.cpp as a
free function template.

Change-Id: Ied32d6e10bb195d111cae7bbcf0e93168118088b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2291
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

tests/net: Working integration tests for HTTP client

This patch is part 1 of 3 with the goal of having a working
integration test harness for BHttpRequest. In this patch the existing
test cases were expanded and fixed for HTTP. In followup patches the
test harness will be updated to support HTTPS and reverse proxies.

Before this patch the tests for BHttpRequest had hard dependencies on
the external services httpbin.org and portquiz.net. These tests
eventually stopped working because the owner of those services made
changes, causing the assertions in these tests to fail.

The goal of these patches is to make a test harness that allows for
the same kinds of end-to-end integration tests but without any
external dependencies.

The test suite now includes a Python script called testserver.py which
is a HTTP echo server of sorts. When it receives a request, it will
echo the request headers and request body back to the client as a
text/plain response body.

The TestServer class manages the lifecycle of this testserver.py
process. Each test case calls Start() on the server to start a new
instance, and then it is shut down when the destructor is called. On
each invocation a random port is assigned by the kernel in TestServer,
and that socket file descriptor is provided to the child testserver.py
script.

Authorization tests are supported, currently implementing Basic and
Digest auth. If the test server receives a request for a path
/auth/<auth-scheme>/<expected-username>/<expected-password>, then the
appropriate authorization scheme will be employed. For example, if
/auth/basic/foo/bar is used as the path, then the server will expect
the Authorization header to contain an appropriate Basic auth
payload.

The tests now perform a bit more validation than before, validating
the expected HTTP headers and response body is returned from the
server.

The following tests are not fixed yet or were removed:
* PortTest was removed entirely since I'm not sure of the point of this
test, and that functionality seems to be covered by the existing tests
anyway.
* HTTPS tests are not functional yet, but will be in a followup
patch. THis requires updating testserver.py to generate a
self-signed TLS cert if --use-tls is provided.
* ProxyTest was disabled before this patch, but can be enabled in a
followup patch by providing a reverse proxy in the test harness.

Change-Id: Ia201ef4583b7636c61e77072a03db936cb0092be
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2243
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>