Fixes case insensitive for resp body

Fixes case insensitive for resp body

Create metadata for a snapshot 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.

DocImpact
Change-Id: I684049412a4aa84f593e970c87157c74fffdfffe
Closes-Bug: #1255917