unit-test: add debug in dependency determination

We are running into a periodic error where 'build_dep_tree' fails
because it is unable to probe the build system used by a dependency.
Add some debug statements so we are able to determine which dependency
this is.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I571d62f191adcab42b4e1814dc6435b1401f3bb8
diff --git a/scripts/unit-test.py b/scripts/unit-test.py
index 1306ddf..f0608bb 100755
--- a/scripts/unit-test.py
+++ b/scripts/unit-test.py
@@ -327,11 +327,16 @@
     # Read out pkg dependencies
     pkg = Package(name, pkgdir)
 
-    for dep in set(pkg.build_system().dependencies()):
+    build = pkg.build_system()
+    if build == None:
+        raise Exception(f"Unable to find build system for {name}.")
+
+    for dep in set(build.dependencies()):
         if dep in cache:
             continue
         # Dependency package not already known
         if dep_added.get(dep) is None:
+            print(f"Adding {dep} dependency to {name}.")
             # Dependency package not added
             new_child = dep_tree.AddChild(dep)
             dep_added[dep] = False