Fix Upstream test cases to be case insensitive

In any domain, due to case sensitivity, if a username
for the project and the username in tempest.conf or
accounts.yaml are not identical, then the test cases
are failing.

So, added .lower() method to change the username strings
to be case insensitive.

Closes-Bug: #1836618

Change-Id: Id7d079c881bbfae972d65ef6049f78da7f25fc1d
1 file changed