Fix loading of much parameters in mcbm2020 unpack macros

• fix name of folder holding the text files
• use different variable name for the two files
• exit with kFALSE if file opening failed
• formatting (tabs, spaces, ...)
• update also the macro for unpacking on mFLES

Unfortunately it was not caught as we do not run any test related to mCBM 2020 in the MR chain. Main changes (folder name and variables names) were tested on kronos.

Refs #1827