docs: update xcat mkchroot for centos8
% begin_ohpc_run
% ohpc_comment_header Create chroot based compute image \ref{sec:assemble_bos}
-\begin{lstlisting}[language=bash,literate={-}{-}1,keywords={},upquote=true,keepspaces,literate={BOSVER}{\baseosshort{}}1]
+\begin{lstlisting}[language=bash,literate={-}{-}1,keywords={},upquote=true,keepspaces,literate={BOSSHORT}{\baseosshort{}}1]
# Save chroot location for compute image
[sms](*\#*) export CHROOT=/install/netboot/BOSVER/x86_64/compute/rootimg/
# Build initial chroot image
-[sms](*\#*) genimage BOSVER-x86_64-netboot-compute
+[sms](*\#*) genimage BOSSHORT-x86_64-netboot-compute
\end{lstlisting}
% end_ohpc_run
