labs: add option for VM gui type

This changeset adds an environment variable and an option that can be
used to change the type of VirtualBox VM GUI used while building the
nodes.

Valid values are gui (default), sdl (minimal gui), and headless.

The resulting node VMs can then be started with or without GUI as
before.

Change-Id: If12f4ba6dc455972b6332318ed1261e2c9de8c3f

labs/lib/osbash/virtualbox.functions

@@ -698,7 +698,11 @@ function vbox_boot {
     local VM=$1
 
     echo >&2 "Starting VM \"$VM\""
-    $VBM startvm "$VM"
+    if [ -n "${VM_UI:-}" ]; then
+        $VBM startvm "$VM" --type "$VM_UI"
+    else
+        $VBM startvm "$VM"
+    fi
 }
 
 #-------------------------------------------------------------------------------

labs/osbash.sh

@@ -56,11 +56,13 @@ function print_config {
         ${OSBASH:+:} echo "no"
 
         echo "VM access method: $VM_ACCESS"
+
+        echo "GUI type: ${VM_UI:-gui}"
     fi
 
 }
 
-while getopts :e:fhnw opt; do
+while getopts :e:fg:hnw opt; do
     case $opt in
         e)
             if [ "$OPTARG" = ova ]; then
@@ -77,6 +79,15 @@ while getopts :e:fhnw opt; do
             wbatch_reset
             unset OSBASH
             ;;
+        g)
+            if [[ "$OPTARG" =~ (headless|gui|sdl) ]]; then
+                VM_UI=$OPTARG
+            else
+                echo "Error: -g argument must be gui (default), sdl, or" \
+                        "headless"
+                exit
+            fi
+            ;;
         h)
             usage
             ;;