Formerly, GPDB do dispatch/interconnect cleanup on executor level
which means once an error occurs within executor, it will be catched and
dispatch/interconnect will be cleaned. The problem is if an error occurs
after an executor started but before the executor run, dispatch/interconnect
has no chance to be cleaned up. A problem is that outbound UDP interconnect
packets still think the interconnect is active and will access the
memory that has been freed.

This commit add a few cleanup points on portal level, a higher call level
than executor to cover more cases shown as above. mppExecutorCleanup() is
reentrant, so it's ok to do double check on both level.