PEM handling of FileNotFound error

[sheggen]

PEM is used to migrate that database, for example in reset_database.sh. When PEM cannot find a migration file (e.g., lsf_migrations/0001_migration_202109241252.py), it throws:

FileNotFoundError: [Errno 2] No such file or directory: 'lsf_migrations/0001_migration_202109241252.py'

The reset_database.sh script should handle this error and avoid crashing the reset, putting the database in an unknown state.