There is an inconsistency for keystone domain names
in the nova doc. ('default' and 'Default')
Replace 'default' with 'Default'.
Change-Id: I437092d04b0cbea78942efd5f565734f34bcbcb2
Closes-Bug: #1821411
(cherry picked from commit a71af2bead)
(cherry picked from commit ef25fff5ec)