* Fix double start for `AbstractEndpoint`
When we use POJO methods in the `IntegrationFlowAdapter`,
the `IntegrationFlowAdapter` is set as a `target` for the `MessagingMethodInvokerHelper`.
When endpoint is started by the application context, such a `start()` is propagated
down to the `MessagingMethodInvokerHelper`.
And in our case back into an `IntegrationFlowAdapter` instance.
This one, in turn, starts its `IntegrationFlow` internally which leads to the
start of the mentioned endpoint in the beginning.
Therefore, we cause a recursive `start()` call on this endpoint from itself.
The `running` flag is set when we are already done with the `doStart()` logic.
Therefore a recursive `start()` call leads to two concurrent polling tasks
in the `AbstractPollingEndpoint`.
* Check also for the `active` flag in the `AbstractEndpoint.start()`
and reset it in case of exception in the `doStart()`
**Cherry-pick to `5.5.x`**
* * Change assert for message timestamps to `isCloseTo()` with percentage
* * Change `catch` in the `AbstractEndpoint.start()` to `RuntimeException`:
the `doStart()` cannot throw unchecked exceptions by definition
* * Fix imports in `AbstractEndpoint`
532692b0ec