m2m_analysis - deal with powergrasp config file creation when launching multiple runs

[ArnaudBelcour]

By default m2m_analysis creates powergrasp config file then deletes it. But this will cause issue when launching multiple runs of m2m_analysis at the same time (the same file being manipulated by different processes). An option preventing the creation of this file (and then asking the user to create this file) should be a way to fix this issue.