Merge connect and handshake timeouts in AbstractIOSessionPool

[rschmitt]

This change essentially reverts a portion of 40cae22 that appears to
have been unnecessary. Since the requestTimeout parameter is always a
connection timeout (at least in the client-side code), we don't need to
dedicate an additional parameter to the TLS handshake timeout value: we
simply use the requestTimeout (which has been renamed connectTimeout
for clarity).

[rschmitt]

I'm not very confident about the rename from requestTimeout -> connectTimeout, because it appears that this parameter sometimes behaves as a connectTimeout and other times behaves as a connectionRequestTimeout. Suggestions and clarifications welcome!

[ok2c]

@rschmitt connectTimeout sounds correct to me. I could not find any evidence of this variable being used as connectionRequestTimeout by AbstractIOSessionPool. Have I missed it somehow?

[rschmitt]

I guess you're right. I suppose that makes sense, since this class is pooling sessions and not connections. (It's just a quirk of terminology that we also "connect" to establish a session.)