Resgate disconnect tests

[jirenius]

Issue

Unit tests should be added to cover ResClient's behavior on unexpected disconnects.

Scope

The tests should describe unexpected disconnect, and test that:

• it does nothing if no subscriptions exists and no requests are pending
• it connects after an unexpected disconnect on first subscription
• it connects after an unexpected disconnect on first call
• it directly attempts to reconnect and resubscribe to existing subscriptions
• it rejects pending requests with a system.connectionError error