[Test-Framework] HttpREquestHelper not compatible with Guzzle 7

[micbar]

Problem

If guzzle encounters some Connection Exceptions, the testsuite throws an PHP Error
and the Details about the Connect Exception are not shown

Incompatibility

This implementation
https://github.com/owncloud/core/blob/master/tests/TestHelpers/HttpRequestHelper.php#L115

is not compatible with guzzle 7

- Function GuzzleHttp\Exception\ConnectException::getResponse() is removed.

from

Guzzle Upgrade Guide
====================

6.0 to 7.0
----------

In order to take advantage of the new features of PHP, Guzzle dropped the support
of PHP 5. The minimum supported PHP version is now PHP 7.2. Type hints and return
types for functions and methods have been added wherever possible. 

Please make sure:
- You are calling a function or a method with the correct type.
- If you extend a class of Guzzle; update all signatures on methods you override.

#### Other backwards compatibility breaking changes

- Class `GuzzleHttp\UriTemplate` is removed.
- Class `GuzzleHttp\Exception\SeekException` is removed.
- Classes `GuzzleHttp\Exception\BadResponseException`, `GuzzleHttp\Exception\ClientException`, 
  `GuzzleHttp\Exception\ServerException` can no longer be initialized with an empty
  Response as argument.
- Class `GuzzleHttp\Exception\ConnectException` now extends `GuzzleHttp\Exception\TransferException`
  instead of `GuzzleHttp\Exception\RequestException`.
- Function `GuzzleHttp\Exception\ConnectException::getResponse()` is removed.
- Function `GuzzleHttp\Exception\ConnectException::hasResponse()` is removed.
- Constant `GuzzleHttp\ClientInterface::VERSION` is removed. Added `GuzzleHttp\ClientInterface::MAJOR_VERSION` instead.
- Function `GuzzleHttp\Exception\RequestException::getResponseBodySummary` is removed.
  Use `\GuzzleHttp\Psr7\get_message_body_summary` as an alternative.
- Function `GuzzleHttp\Cookie\CookieJar::getCookieValue` is removed.
- Request option `exception` is removed. Please use `http_errors`.
- Request option `save_to` is removed. Please use `sink`.
- Pool option `pool_size` is removed. Please use `concurrency`.
- We now look for environment variables in the `$_SERVER` super global, due to thread safety issues with `getenv`. We continue to fallback to `getenv` in CLI environments, for maximum compatibility.
- The `get`, `head`, `put`, `post`, `patch`, `delete`, `getAsync`, `headAsync`, `putAsync`, `postAsync`, `patchAsync`, and `deleteAsync` methods are now implemented as genuine methods on `GuzzleHttp\Client`, with strong typing. The original `__call` implementation remains unchanged for now, for maximum backwards compatibility, but won't be invoked under normal operation.
- The `log` middleware will log the errors with level `error` instead of `notice` 
- Support for international domain names (IDN) is now disabled by default, and enabling it requires installing ext-intl, linked against a modern version of the C library (ICU 4.6 or higher).

[micbar]

@phil-davis Can a qa engineer check this out?

[phil-davis]

Should be fixed by #39251 - I will bump the core commit id in oCIS so that he change gets run in oCIS CI.