[Provisioner] Instructor_inventory to closely match student_instance_inventory

[nicholas-chia]

…ce_inventory

This update makes the instructor inventory clearer by explicitly stating username and admin_password to the inventory for each student login.

I usually upload instructor inventory to gist during workshop. Removes ec2-user to avoid any confusion.

[gundalow]

@nicholas-chia Looks like you have unrelated commits in here