Fixes case insensitive for resp body

Create metadata for a volume with key-value set, which key in uppercase
and lowercase(e.g.{"key": "v1", "KEY": "V1"), the server accept the
request and return the key-value set {"key": "v1", "KEY": "V1"}. But the
server just add one metadata because the server is not case sensitive.

The patch will modify the resp body with the one which the server added.

update_all has the same ploblem.

Fixes errors on v2 unittest without difficulty.

DocImpact
Closes-Bug: #1258004

Change-Id: Ic337c0a351ac234493e1d73b86ba87520f32289a
Merge "Fixes case insensitive for resp body"