metest/add_packages.py: add explanation why there might be no artifacts

Signed-off-by: Robert Eckelmann <longnoserob@gmail.com>

mrtest/add_packages.py

@@ -115,13 +115,13 @@ def add_packages(origin, mr_id, no_cache):
 
     try:
         zip_path = mrhlpr.mr.get_artifacts_zip(mr_id, no_cache, origin)
-    except HTTPError:
-        print(
-            """
-Remote server does not have any packages to download.
-Please trigger again the MR {} to generate the packages.
-""".format(mr_id)
-        )
+    except (HTTPError, AttributeError):
+        print(f"\r\nRemote server does not have any packages to download for MR {mr_id}!")
+        print("\r\nThis could be caused by:")
+        print(" * use of [CI:skip-build] in the last commit")
+        print(" * CI pipeline failure")
+        print(" * MR is in draft status and pipelines have not run yet.")
+        print(f"Please trigger again the MR {mr_id} to generate the packages.\r\n")
         exit(0)
 
     selection = mrtest.select_package.ask(zip_path)