Updating SwiftOnFile version to release 2.0

Updated sof version and tox swift dependency to
release 2.0.
Also, made some documentation changes to the object-server
configuration sample file to point out that volume must
mounted before starting sof object-server.

Signed-off-by: Thiago da Silva <thiago@redhat.com>
Merge pull request #33 from thiagol11/release2.0

Updating SwiftOnFile version to release 2.0