JIRA: https://jira.spring.io/browse/INT-4028
Previously the `ClientWebSocketContainer` after the connection failure couldn't be restored even after `stop()/start()`
because the `openConnectionException` property hasn't been clear on `stop()`
* Add `openConnectionException = null` to `stopInternal()` logic
* Also clear `openConnectionException` and `clientSession` on `start()`
* Plus add recovery (restart) logic into the `getSession()` if the `!clientSession.isOpen()`
**Cherry-pick to 4.2.x**
Fix race condition around `start/stop`
The new `start/stop` logic brakes the in-flight connection.
* Introduce one more `connecting` flag to indicate that we are in connecting process.
* Absorb the a new test for `ClientWebSocketContainer` with the existing one. Looks like there is some extra session close in between.
* Adjust timeouts in the `StompIntegrationTests` to 20 secs. Add `org.apache.catalina` category for tracing logs
39ee4ea3b6