[Fix] MySQLdb errors fixed

[BLasan]

Description
MySQLdb module member errors in UserManager.py and DownloadManager.py fixed.

Related Issue
#902

Motivation and Context
Code should be bug free. No errors should be occured.

How Has This Been Tested?
Open UserManager.py and DownloadManager.py and the errors will be underlined with red lines.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[kmehant]

@BLasan Can you now pull the updated pr branch from here and squash all your commits keeping only the relevant changes and force push it to here.

[BLasan]

@kmehant Please review