Adapted opt_perforce_sdp_backup service to work with SELinux in
enforcing mode.
Added logic from sdp_upgrade.sh that installs SDP the backup
service into install_sdp.sh.
With this adjustment, the service now specifies the "on disk"
location of the file; no symlinks are allowed in the absolute
path to the script (to keep SELinux happy). For clarity,
'User=root' was added to the systemd service file for the
backup utility.