newvm: Avoid adding graphics adapter by default

VMs don't really need graphical consoles; serial terminals are good
enough, or even better given that they are logged.  For the few cases
where a graphical console is actually necessary, the `newvm.sh` script
can add one with the `--graphics` argument.

newvm.sh

@@ -12,6 +12,7 @@ network=network=kube
 dnsdomain=host.pyrocufflink.black
 console=true
 default_groups=true
+graphics=false
 
 usage() {
     printf 'usage: %s [options] name\n' "${0##*/}"
@@ -76,6 +77,9 @@ while [ $# -gt 0 ]; do
     --domain=*)
         dnsdomain=${1#=*}
         ;;
+    --with-graphics)
+        graphics=true
+        ;;
     --cfg-branch)
         shift
         cfg_branch=$1
@@ -105,6 +109,7 @@ while [ $# -gt 0 ]; do
             name="$1"
         else
             usage >&2
+            printf 'unknown option: %s\n' "${1}" >&2
             exit 2
         fi
     esac
@@ -183,6 +188,10 @@ if [ -n "${cfg_branch}" ]; then
     set -- "$@" --qemu-commandline="-fw_cfg opt/dch/cfg-branch,string=${cfg_branch}"
 fi
 
+if ! $graphics; then
+    set -- "$@" --graphics=none
+fi
+
 if $console; then
     set -- "$@" --autoconsole text
 else