Add some more context on why certain tests are failing

tests/test_vms_platform.py

@@ -80,7 +80,7 @@ def _validate_apt_sources(self, vm):
         stdout, stderr = vm.run(cmd)
         contents = stdout.decode("utf-8").rstrip("\n")
 
-        self.assertTrue(self.apt_url in contents)
+        self.assertIn(self.apt_url, contents, f"{vm.name} missing apt sources list")
 
     def _ensure_packages_up_to_date(self, vm, fedora=False):
         """
@@ -101,7 +101,10 @@ def _ensure_packages_up_to_date(self, vm, fedora=False):
         else:
             cmd = "sudo dnf check-update"
             # Will raise CalledProcessError if updates available
-            stdout, stderr = vm.run(cmd)
+            try:
+                stdout, stderr = vm.run(cmd)
+            except subprocess.CalledProcessError:
+                self.assertTrue(False, fail_msg)
             # 'stdout' will contain timestamped progress info; ignore it
             results = stderr.rstrip().decode("utf-8")
             stdout_lines = results.split("\n")