always log output to a file

This eliminates the risk of losing crucial debug output in a
long mkcloud run because you forgot to redirect to a file and
the terminal/screen/tmux scrollback buffer wasn't big enough.

Closes #1191.

scripts/mkcloud

@@ -28,6 +28,12 @@ for required_var in cloud; do
     fi
 done
 
+: ${log_dir:=/var/log/mkcloud/$cloud}
+mkdir -p "$log_dir"
+log_file=$log_dir/`date -Iseconds`.log
+exec >  >(tee -ia $log_file)
+exec 2> >(tee -ia $log_file >&2)
+
 if [[ $debug_mkcloud = 1 ]] ; then
     set -x
     PS4='+(${BASH_SOURCE##*/}:${LINENO}) ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'