Remove suffix "JSON" from Nova v3 API last test class

We have decided that XML support is removed from Nova v3 API and
the tests also has been removed from Tempest already.
Then the suffix "JSON" of Nova v3 API test classes does not have
any meanings.

This patch removes them for cleanup. This is made because of a
comment of Ie3c595fb77143e58e30404c42f358d6443a52c0b .

NOTE: Most of the test classes already don't have the suffix
"JSON" with this: Ic7372817777256ce723843ffd3e0bc670261aa78 .
This is the last one of having the suffix "JSON" of Nova v3 API
test class.

Part of bp:remove-v3-xml-api

Change-Id: I6ce769eaed89ef46f0c488ab99b5ed674f2f53a2
Merge "Remove suffix "JSON" from Nova v3 API last test class"