Add failpoint tests to result spooling code

IMPALA-8924 was discovered while running test_failpoints.py with results spooling enabled. The goal of this JIRA is to add similar failpoint coverage to test_result_spooling.py so that we have sufficient coverage for the various failure paths when result spooling is enabled.

The failure paths that should be covered include:

• Failures while executing the exec tree should be handled correctly