Fallback to default name if none provided, same as other vars

Author: CoolUsername

src/mbed_os_tools/test/host_tests_runner/mbed_base.py

@@ -88,6 +88,11 @@ def get_remount_count(disk_path, tries=2):
             """! Get the remount count from 'DETAILS.TXT' file
             @return Returns count, None if not-available
             """
+
+            #In case of no disk path, nothing to do
+            if disk_path is None:
+                return None
+                
             for cur_try in range(1, tries + 1):
                 try:
                     files_on_disk = [x.upper() for x in os.listdir(disk_path)]