Enhance pbs_snapshot to be non-root friendly

Motivation:

pbs_snapshot was only supported as being run by root user because it needed to capture protected data (like sched_priv, server_priv, etc.). This means that any automated script, PTL test or other program that wants to use pbs_snapshot was also needed to be run as root. So, making it non-root friendly removes this restriction.

Design Discussion:

http://community.pbspro.org/t/running-pbs-snapshot-with-sudo/786

Interface Changes:

New option to pbs_snapshot "--with-sudo":

• When provided, pbs_snapshot will use PTL's sudo infrastructure to run necessary commands and copy protected files via sudo.

• When using this option, the user doesn't need to run pbs_snapshot itself with sudo (i.e, no need to do "sudo pbs_snapshot ... "), or run it as root user.

• This option is turned off by default.

• If your sudo rules reject any of the commands being run with sudo by pbs_snapshot, it will log "ERROR" type log messages for them and move on to capturing whatever data it can.

• Example usage: pbs_snapshot -o $HOME --with-sudo