Non-default settings of AuthInfo fix

We are using a non-default AuthInfo configuration and based on
log-messages we see I believe this is not properly handled in certain
parts of the code.

Typical log message:
Aug 12 17:06:15 t02n20 slurmd[27001]: error: Munge encode failed:
Failed to access "/var/run/munge/munge.socket.2": No such file or
directory
Aug 12 17:06:15 t02n20 slurmd[27001]: error: Creating authentication
credential: Socket communication error
Aug 12 17:06:15 t02n20 slurmd[27001]: error: stepd_connect to 3165.0
failed: Protocol authentication error
Aug 12 17:06:15 t02n20 slurmd[27001]: error: If munged is up, restart
with --num-threads=10