Moving READTHEDOCS application settings to RTD prefix for docker only

[Iamshankhadeep]

Fixes #5586

[saadmk11]

You may want to change the names in all other places they are used in the repository otherwise you will get errors like AttributeError: 'Settings' object has no attribute 'DOCKER_IMAGE'

[Iamshankhadeep]

@saadmk11 I changed all the variable name that required and after running python manage.py loaddata test_data I am getting a output like this Installed 23 object(s) from 1 fixture(s) no errors shown. But why travis ci build is failing?

[saadmk11]

@Iamshankhadeep you can check the error logs from travis or you can run tests locally to see whats breaking. After seeing the error log I can see that some files are still trying to access old variable name like config/tests/test_config.py.