Don't check $LOCKEDUSERS at all, instead fall back to userslot 2 as a last resort if the user doesn't already exist, and the automatic slot detection doesn't find an unlocked slot. This is essentially what was happening in the older version of the script before #6380 as $LOCKEDUSERS was only ever referenced here.
Also move setting the username before setting privileges and access levels, as those steps fail if done before username is set for the slot.
Instead of relying on hard coded offsets, query each slot's status with ```ipmitool channel getaccess``` and use the first slot that is unlocked.
This fixes an issue on certain Cray x86 nodes that have arbitrary locked IPMI user slots.
RH7/Centos7 and recent versions of fedora relocate `/*bin/*` into `/usr/*bin/`. This causes
conflicts for upgrades against xCAT-genesis-scripts-* packages which expect the `/bin` a to be
a directory while `xCAT-genesis-base-*` packages provide a link. Relocating all files into `/usr`
fixes that conflict and allows a clean upgrade from all old versions.
