Consider cmscp EC 60307 (stageout failure) as recoverable error. Fix exit code and msg in job report from cmscp.

In https://github.com/dmwm/CRABServer/issues/4569, there are two things to fix:
1) exit code 60307 should be recoverable, not fatal;
2) you see that the exit code is not 0, but Exit message says: "ok". This is because the exit message in the job report was not modified by cmscp. Only the exit code was modified.

This PR fixes these two issues.