RANGER-5147: Modernize some Python scripts now that Python 3 is a requirement

[HalimKim]

What changes were proposed in this pull request?

• in db_setup.py script, there's subprocess.Popen function.
• From python 3, the stdout of Popen instance is byte by default. it means it is not str anymore
• So if you are trying to execute this script, you will see error below

TypeError: a bytes-like object is required, not 'str'

• To avoid this problem, simply just add text=True option in Popen()

How was this patch tested?

• Manually Tested.