Add system-info Linux systemd user unit

Update the `system-info` directory with the addition of a `systemd`
service file and an new Linux script to display current CPU temperature
and core/thread utilization. Update `.conduit.yaml` with addition
`apt` dependencies `sysstat` and `jq`. Update the install and remove
scripts to setup and tear down the `systemd` user unit. Lastly, decrease
the `tmux` status line update interval from 5 to 2 seconds.

system-info/system-info-Linux.sh

@@ -9,7 +9,8 @@ if [ ! -d $cache_dir ]; then
 fi
 
 # Cleanup cache file when interrupted.
-trap '[ -f $cache_file ] && rm $cache_file;' INT
+trap '[ -f $cache_file ] && rm $cache_file; exit' INT
+trap '[ -f $cache_file ] && rm $cache_file; exit' TERM
 
 while true; do
   # Parse the current CPU load on all cores/threads.
@@ -17,8 +18,7 @@ while true; do
     jq '.sysstat.hosts[0].statistics[0]["cpu-load"][1:]|.[].idle' | \
     awk '$idle ~ /[-.0-9]*/ { printf "%s", substr("█▇▆▅▄▃▂▁ ", int($idle / 11), 1) }'`
   # Parse the current CPU package temperature.
-  cpu_temp=`sensors coretemp-isa-0000 | head -3 | tail -1 | \
-    awk '{ print substr($4, 2) }'`
+  cpu_temp=`sensors coretemp-isa-0000 | awk 'NR == 3 { print substr($4, 2) }'`
   # Write to the cache file.
   echo "$cpu_temp $cpu_load" > $cache_file
 done