There was some confusion/debate in reviewing
I5fa1fdba56803b2ef63b1efaaeeced6ceb7779d9 and whether or
not it required a microversion to change the response code.
This was a pretty common sense scenario where 415 was a
more appropriate error code for 400 and is a better client
experience when hitting that error.
This change updates the potentially confusing part of the
devref about this and adds a note to ask the Nova API
subteam when in doubt about whether or not a microversion
is needed for changing error codes.
Change-Id: I8a2836076b7fadc697bdc013578c3d777d02a833
Related-Bug: #1567977
e781103841