fix(basic-install): unattended install should finish without interaction

Fixes: https://github.com/pi-hole/pi-hole/issues/3617

Signed-off-by: Grégory Sanchez <gregory.sanchez@icloud.com>

automated install/basic-install.sh

@@ -67,7 +67,9 @@ PI_HOLE_INSTALL_DIR="/opt/pihole"
 PI_HOLE_CONFIG_DIR="/etc/pihole"
 PI_HOLE_BIN_DIR="/usr/local/bin"
 PI_HOLE_BLOCKPAGE_DIR="${webroot}/pihole"
-useUpdateVars=false
+if [ -z "$useUpdateVars" ]; then
+  useUpdateVars=false
+fi
 
 adlistFile="/etc/pihole/adlists.list"
 # Pi-hole needs an IP address; to begin, these variables are empty since we don't know what the IP is until