Enhance pre-flight check on EC-Switch-SECLOG.py script

[silavjy]

Check if all Cloudformation stacks are in create complete or update complete status before running the migration process.

When running the script on 2 accounts found that someone has tried to update some stacks and left them in a status failed - therefore the script failed. To prevent this, do a first check on all the stacks to be updated to make sure no errors will happen for these cases.