After restarting from a checkpoint image, AthenaMP first updates some of
the configuration parameters (e.g. input file, output file, max events)
from runargs file in the master run directory and only after that
proceeds with forking worker processes.

At this point implemented only the mechanism that allows changing the number
of workers. Transform updated such that the number of workers gets written
out to runargs file, and AthenaMP picks this number from there.


Former-commit-id: 1385252f5c74f4554a929ffc5496f61257ad454f