Error out if run from the wrong directory

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/scripts/run_demos.py

@@ -43,6 +43,8 @@ def run_all_demos(quiet=False):
     Return True if all demos passed and False if a demo fails.
     """
     all_demos = glob.glob('programs/*/*_demo.sh')
+    if not all_demos:
+        raise Exception('No demos found. run_demos needs to operate from the Mbed TLS toplevel directory.')
     return run_demos(all_demos, quiet=quiet)
 
 def main():