Irace output dir logic

[DE0CH]

To contain everything irace and the calling code generate, they are all put inside irace_output directory. Currently, irace_output is hard coded in some places (and not in some other). Also calling irace with subprocess is done in cwd of irace_ouput, resulting in sometimes needing to to os.basename(...) and other time irace_output/..., depending on if the file name contains is relative to the root folder or irace_output folder. Need to pick one and make them consistent.