Switch to using bash traps to destroy bhyve vms.

ansible/roles/bhyve/files/bhyve_netgraph_bridge.bash

@@ -35,6 +35,33 @@ if [ "$VERBOSE" = "YES" ]; then
     set -x
 fi
 
+############## Setup #########################
+
+function cleanup {
+    for vm in "${vms[@]}"; do
+        log "Destroying bhyve vm $f"
+        bhyvectl "--vm=$vm" --destroy
+        log "Destroyed bhyve vm $f"
+    done
+}
+vms=()
+for sig in EXIT INT QUIT HUP TERM; do
+  trap "set +e; cleanup" "$sig"
+done
+
+function die {
+    local status_code="$1"
+    shift
+    (>&2 echo "${@}")
+    exit "$status_code"
+}
+
+function log {
+    (>&2 echo "${@}")
+}
+
+############## Program #########################
+
 function main {
     local cmd="$1"
     shift 1
@@ -122,6 +149,7 @@ function start_vm {
     if [ "$VNC_ENABLE" = "YES" ]; then
         additional_args+=("-s" "29,fbuf,tcp=$VNC_LISTEN,w=1920,h=1080")
     fi
+    vms+=("$name")
     while true; do
         set -x
         set +e
@@ -156,9 +184,6 @@ function start_vm {
             break
         fi
     done
-
-    bhyvectl "--vm=$name" --destroy
-    echo "Destroyed bhyve vm."
 }
 
 function detect_available_link {