Update install_prodstack.rst

After installing Fullstack via Vagrant, the user needs to know the credentials to login to edX
Merge pull request #4507 from dmin7b5/patch-1

Update install_prodstack.rst
BLD-1104: List units that use group configuration.
Merge pull request #4528 from edx/jmclaus/edit-group-configurations-usage

BLD-1104: List units that use group configuration.
BLD 1020: Easy access to Group Configurations page from Content Experiment component.
Fix logic.
Fixed error.