HTTP1ConnectionsProvider.state needs to become `private`

[weissi]

Right now, HTTP1ConnectionsProvider.state is internal and some tests modify the state without HTTP1ConnectionsProvider knowing about this.

That cannot be right because HTTP1ConnectionsProvider cannot clean up stuff it didn't know happened. Therefore we see extremely fragile and ugly cleanup code in some tests.

[weissi]

when this is fixed, HTTP1ConnectionProvider.closePromise must become private too, there's no reason for the tests to fulfil internal promises of the provider.