improved test_tmpfs to delete the stresser file if it alraeady exists when launching the test

src/test_tmpfs.py

@@ -17,6 +17,8 @@ def measure_tmpfs_impact(file_size_in_mib: int):
     '''measures the effect of tmpfs file on meminfo variables
     '''
     stresser_file_path = Path('/dev/shm/tmpfs-stresser.bin')
+    if stresser_file_path.exists():
+        stresser_file_path.unlink()
 
     ramana_out_root = Path('./ramana-out')
     ramana_out_root.mkdir(exist_ok=True)