Make general.prompt optional

src/config/general.rs

 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 pub struct GeneralConfig {
-    pub prompt: bool,
+    pub prompt: Option<bool>,
     // Allow config to specify cookbook recipe or binary package as default
     pub repo_binary: Option<bool>,
     pub efi_partition_size: Option<u32>, //MiB
@@ -8,7 +8,7 @@ pub struct GeneralConfig {
 
 impl GeneralConfig {
     pub(super) fn merge(&mut self, other: GeneralConfig) {
-        self.prompt = other.prompt;
+        self.prompt = other.prompt.or(self.prompt);
         self.repo_binary = other.repo_binary.or(self.repo_binary);
         self.efi_partition_size = other.efi_partition_size.or(self.efi_partition_size);
     }

src/lib.rs

@@ -150,7 +150,7 @@ pub fn install_dir<P: AsRef<Path>, S: AsRef<str>>(config: Config, output_dir: P,
     //let mut context = liner::Context::new();
 
     macro_rules! prompt {
-        ($dst:expr, $def:expr, $($arg:tt)*) => (if config.general.prompt {
+        ($dst:expr, $def:expr, $($arg:tt)*) => (if config.general.prompt.unwrap_or(true) {
             Err(io::Error::new(
                 io::ErrorKind::Other,
                 "prompt not currently supported"
@@ -186,7 +186,7 @@ pub fn install_dir<P: AsRef<Path>, S: AsRef<str>>(config: Config, output_dir: P,
         // plaintext
         let password = if let Some(password) = user.password {
             password
-        } else if config.general.prompt {
+        } else if config.general.prompt.unwrap_or(true) {
             prompt_password(
                 &format!("{}: enter password: ", username),
                 &format!("{}: confirm password: ", username))?