Update glexecComputingElement.py

Status codes < 127 mean glexec worked but the script it ran produced an error. This change allows Application Failed with Errors results to show through, rather than be masked by false "glexec CE submission" errors.
Merge pull request #1916 from Andrew-McNab-UK/rel-v6r10

[v6r10] Update glexecComputingElement.py