Clean up in test_server_diagnostics unit test case

This patch changes V3 router to V21 router,
and HTTPRequestV3 to HTTPRequest. which can be shared between
V21 and V2

Partially implements blueprint v2-on-v3-api
Change-Id: Id3c91c377b9ba98c5cf2d1d2b4f476cec3159792
Use HTTPRequest instead of HTTPRequestV3 for v2/v2.1 tests

This patch replace HTTPRequestV3 with HTTPRequest for
test_shelve unit test case, which can be shared between
v2 and v21

Partially implements blueprint v2-on-v3-api
Change-Id: I732335e1f4885a067e42c48c75417ba0b4aba192
Merge "Clean up in test_server_diagnostics unit test case"
Merge "Use HTTPRequest instead of HTTPRequestV3 for v2/v2.1 tests"