Adds test for list/get volume attachments V2 APIs

This patch adds the test for following Nova V2 APIs-
- List volume attachments
- Get volume attachment
Response Schema has been added for the same.

To make consistent in server_client and easy for tests to compare
the response, this Patch also change the returned response body from
server_client's attach_volume().

Note- XML test cases is not implemented as it is deprecated.
New test cases has been skipped for XML.

Change-Id: Iee055ceaad135bba4a57b010d1e08652e2d13598
javelin2: destroy functions above network resources

Implements functions for removal of following resources:
 - networks
 - subnets
 - routers
 - security groups

Change-Id: I447deaa9f320116fc22bb0222eedee10af2f4c59
Partial-Bug: 1330178
Merge "Adds test for list/get volume attachments V2 APIs"
Merge "javelin2: destroy functions above network resources"