Improvements to import_data script following a migration from 2.2.2 to 2.5.1

[mjsqu]

Following a successful migration from v2.2.2 to v.2.5.1 I have submitted an updated import_db.py script with some improvements that we found useful when running our migration. See the update list below.

…sts - update comments

Issue #, if available: N/A

Description of changes:

• Addition of sleep statement to prevent throttling errors when reading CloudWatch
• Removal of the import_db DAG from the getDagTasks query - as import_db DAG most probably doesn't exist on the source environment
• More print statements in the CloudWatch migration to track progress
• Check to see if variable.csv file exists before reading - some source environments have no variables so this file may not exist

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[umaragu]

The changes will impact the 2.4.3 migration. We need new files for 2.2.2 to 2.5.1 migration

[mjsqu]

In my opinion the import_data.py code would probably work on 2.4.3 or 2.5.1 - if you test that on both versions then all that's left to do is complete the picture with an export_data.py for getting data out of 2.4.3.

[mjsqu]

This can be closed, the codebase has moved on a few versions