Update quictestlib to not require tserver

[mattcaswell]

On the feature/quic-server branch we should update functions such as qtest_create_quic_objects in test/helpers/quictestlib.c to not require tserver, but instead use the normal QUIC API.

tserver only exists because we originally only had client side code, and we needed a simple server implementation to tun our tests against. Now the the feature/quic-server branch has a full server implementation in it we should be using that for our tests.

This issue is to provide the necessary test framework support to enable new tests in quicapitest.c to be written without any dependence on tserver. A separate issue will be created to convert existing tests to remove the dependency on tserver.

Eventually we should be able to remove tserver completely.

To resolve this issue we should:

• Review all functions in test/helpers/quictestlib.c that use QUIC_TSERVER
• For all functions we should implement an alternative that does not have a dependence on QUIC_TSERVER
• We should convert 1 or 2 tests in quicapitest.c to use the new functions to confirm that they work as expected