change stepchain timeperevent calculation

[z4027163]

Change the way of calculation time/event of stepchain. So far it does the same factorization on generator task.

[haozturk]

I fixed the infinite loop and injected 17 production workflows w/ this code. I updated the stepchain params as 1 core and 2.3GB memory. Here is the list of those workflows:

haozturk_task_HIG-RunIISummer15wmLHEGS-05254__v1_T_211201_110932_7311
haozturk_task_HIG-RunIISummer15wmLHEGS-05242__v1_T_211201_110937_2314
haozturk_task_HIG-RunIISummer15wmLHEGS-05253__v1_T_211201_110942_1488
haozturk_task_HIG-RunIISummer15wmLHEGS-05252__v1_T_211201_110946_5243
haozturk_task_HIG-RunIISummer15wmLHEGS-05259__v1_T_211201_110951_1345
haozturk_task_HIG-RunIISummer15wmLHEGS-05239__v1_T_211201_110955_9970
haozturk_task_HIG-RunIISummer15wmLHEGS-05241__v1_T_211201_111000_1999
haozturk_task_HIG-RunIISummer15wmLHEGS-05255__v1_T_211201_111004_3802
haozturk_task_HIG-RunIISummer15wmLHEGS-05240__v1_T_211201_111009_174
haozturk_task_HIG-RunIISummer15wmLHEGS-05243__v1_T_211201_111013_3554
haozturk_task_HIG-RunIISummer15wmLHEGS-05251__v1_T_211201_111017_8519
haozturk_task_HIG-RunIISummer15wmLHEGS-05257__v1_T_211201_111022_7229
haozturk_task_HIG-RunIISummer15wmLHEGS-05250__v1_T_211201_111027_7091
haozturk_task_HIG-RunIISummer15wmLHEGS-05232__v1_T_211201_111032_4342
haozturk_task_HIG-RunIISummer15wmLHEGS-05258__v1_T_211201_111037_127
haozturk_task_HIG-RunIISummer15wmLHEGS-05256__v1_T_211201_111041_9248
haozturk_task_HIG-RunIISummer15wmLHEGS-05238__v1_T_211201_111046_7657

I want to see how these workflows perform, so let's keep the PR open. TimePerEvent calculation seems accurate. I see one problem:

• There is a events_per_job check. We should have a lower limit and not convert workflows below it.