Fix CMSSW diagnostics of segfaults

When a SEGFAULT occurs in cmsRun, the process exits with a 134
error code and leaves an empty FrameworkJobReport behind,
the same case as when the cmsRun process receives a SIGKILL or SIGTERM.
The empty FWJR caused the diagnostics handler to crash and therefore
the job didn't do the logArchive step or returned the report pickle,
this patch fixes that and extends the unti tests for the CMSSW executor
with diagnostics.

Fixes #4134