CXF-7996: TCK Fixes for SSE reconnect state tests

[andymc12]

This should resolve at least one of the failing SSE tests (specifically, defaultWaiting1s_from_standalone). The TCK is very picky about the isOpen method - and the behavior of the SseEventSource is not terribly intuitive. While the "state" of the SseEventSource might be CLOSED or CONNECTING, the TCK still expects that the isOpen method will return true until it has been explicitly closed (via the close method). I adjusted the unit tests to expect this distinction - but also to continue testing for the proper state of the SseEventSource.

[andymc12]

Thanks for the approval - it looks like these changes may be causing some systest failures - some of them seem unrelated, but others are in the SSE bucket - I'll investigate a little more - it's possible I may need to tweak the tests.