system-image: implement auto confirm / reject feature

This is intended for use in server environments, in the installer, and any
situation where you don't want a prompt on the TTY at shutdown/reboot.

usr/local/sbin/system-image

@@ -16,7 +16,15 @@ function echo_tty {
   fi
 }
 
+AUTO_CONFIRM="false"
+AUTO_REJECT="false"
 function yesno {
+  if "$AUTO_CONFIRM"; then
+    return 0
+  fi
+  if "$AUTO_REJECT"; then
+    return 1
+  fi
   unset DISCARD_ME
   while [ -z "$DISCARD_ME" ]; do
     echo_tty -n "[y/n] "
@@ -43,10 +51,14 @@ function yesno {
 #TODO: refuse to run if system is running
 
 if [ "$1" = "--yes" ]; then
-  DONT_ASK="true"
+  AUTO_CONFIRM="true"
+else
+  if [ -e "/run/void-usb/system-image-auto-confirm-marker" ]; then
+    AUTO_CONFIRM="true"
+  else
+    if [ -e "/run/void-usb/system-image-auto-reject-marker" ]; then
+      AUTO_REJECT="true"
     else
-  DONT_ASK="false"
-
       #TODO: use a bright color for ==== and the question
       echo_tty "=========================="
       echo_tty "Create a new system image?"
@@ -62,8 +74,13 @@ else
       echo_tty "Creating a new system image will take some time."
       echo_tty
     fi
+  fi
+fi
 
-if $DONT_ASK || yesno; then
+if yesno; then
+  echo_tty "=========================="
+  echo_tty "Building new system image."
+  echo_tty "=========================="
   echo_tty -n "Generating exclusion list... "
   # cutting off the leading slash allows us to just ignore empty lines below
   readarray -t MOUNT_LIST <<< "$(findmnt --output TARGET --noheadings --raw | sed -e 's|^/||' | sort)"
@@ -107,7 +124,9 @@ if $DONT_ASK || yesno; then
     echo_tty "done"
   fi
 else
+  echo_tty "=========================="
   echo_tty "Discarding system changes."
+  echo_tty "=========================="
 fi
 
 echo_tty -n "Syncing... "