Correct the keypairs-get-resp.json API sample file

Current keypair sample files 'keypairs-get-resp.json/xml contain
'keypairs' as the first key and that means its sample response
of "list keypairs" API not "get keypair" API.

The tests don't pass a keypair id, so current tests also are for
"list keypairs" API.

Details-
Below API sample files- from their name it looks like these are for
get keypair API. But in actual content of these files are written as
List keypair API response. So it create the confusion that for which
API these API sample file are. Name suggest for GET and content
suggest for LIST Keypair.

    /nova/tests/integrated/api_samples/os-keypairs/
    keypairs-get-resp.json.tpl
    /nova/tests/integrated/api_samples/os-keypairs/
    keypairs-get-resp.xml.tpl

Their API sample test cases are written corrosponding to list keypair
APIs.

This patch correct the above API sample file name from get to list
Keypair APIs.
API Sample test cases names are also modified accordingly.

Partial-Bug: 1298769

Change-Id: I88d894ff9b0f6236221fa922601b641f26a87301
Merge "Correct the keypairs-get-resp.json API sample file"