ensure blob directory exists in archives

[gjcolombo]

The helios-omicron-brand code that unpacks zone images requires all file entries in an archive to be preceded by entries that create those files' directories. Ensure the packaging code adds the requisite entries for downloaded blobs (as it already does for Rust programs).

Propolis will need a patch release containing this fix to produce functioning Omicron zone images, so I've bumped the package version to 0.12.2 in this commit; let me know if I should do that in a separate PR.

Tested by building a Propolis package using this commit and verifying that (a) tar -tzf prints the appropriate output structure, and (b) hotpatching an Omicron dev cluster with this zone image allows instances to start (images created without the fix produce a file-not-found error when sled-agent tries to start them).

[gjcolombo]

Whoops. Will look at the test failures when I get a minute.

[smklein]

I believe tests are failing because we're adding these directories, even if no blob inputs actually exist

[smklein]

The following change works for me:

     fn get_blobs_inputs(&self, download_directory: &Utf8Path, zoned: bool) -> Result<BuildInputs> {
         let mut inputs = BuildInputs::new();
 
+        let s3_blobs = self.source.blobs();
+        let buildomat_blobs = self.source.buildomat_blobs();
+        let any_blobs = s3_blobs.is_some() || buildomat_blobs.is_some();
+
         let destination_path = if zoned {
-            zone_archive_path(
-                &Utf8Path::new("/opt/oxide")
-                    .join(self.service_name.as_str())
-                    .join(BLOB),
-            )?
+            let dst = Utf8Path::new("/opt/oxide")
+                .join(self.service_name.as_str())
+                .join(BLOB);
+
+            // Add the parent input directories to ensure they exist
+            // before adding the blobs themeselves.
+            //
+            // However, only do this work if the blobs actually exist.
+            if any_blobs {
+                inputs.0.extend(
+                    zone_get_all_parent_inputs(&dst)?
+                        .into_iter()
+                        .map(BuildInput::AddDirectory),
+                );
+            }
+
+            zone_archive_path(&dst)?
         } else {
             Utf8PathBuf::from(BLOB)
         };
-        if let Some(s3_blobs) = self.source.blobs() {
+        if let Some(s3_blobs) = s3_blobs {
...
-        if let Some(buildomat_blobs) = self.source.buildomat_blobs() {
+        if let Some(buildomat_blobs) = buildomat_blobs {

[gjcolombo]

Thanks! Fixed in a0e6bbf, though I opted just to short-circuit the entire routine if there are no blobs to add. Let me know if you'd prefer an approach like the one you've outlined--I mostly went with short-circuiting because it seemed a bit sad to go through all the path computations unconditionally only to find out that we'll never use them because there's nothing to add.

[gjcolombo]

Thanks for the fast turnaround, @smklein!