Improve receiveMessages() error and interrupt handling

This message source is now implemented asynchronously, which is why
the `pollPeriod` parameter has been removed.
Restore and "deprecate" pollPeriod parameter

This preserves backwards compatibility. We should find a better
way to actually deprecated parameters/operations/etc.
Update CHANGELOG.md for 2.5.1 release
Merge pull request #12 from mulesoft/CLDCONNECT-1424

Improve receiveMessages() error and interrupt handling