Optionally manage TMOUT in simp.sh.erb

[nick-markowski]

We may want to manage some settings in simp.sh.erb but not manage TMOUT. For instance, if another file in /etc/profile.d manages TMOUT and it's read only, depending on the order of the file read-in, users will be greeted with a read-only warning on log-in that may not be desirable.

<% if @manage_tmout then -%>
[ $TMOUT ] || export TMOUT=<%= @session_timeout.to_i * 60 %>
readonly TMOUT
<% end -%>