Raise more information on V2 API volumes when resource not found

NotFound exception is caught in volumes.py on v2 api
and raise HTTPNotFound exception but exception information are
not well specified. This patch adds more information
to the raised exception.

Change-Id: I2bd48503460662fcc648b31ade7156059b370f2b
Closes-Bug: #1275755
Merge "Raise more information on V2 API volumes when resource not found"