Scality driver:use self.configuration instead of CONF

In order for the Filter scheduler to be used to it's full advantage
Cinder drivers need to move away from using FLAGS directly and switch
to appending their specific options to self.configuration.

This patch converts the driver and updates tests.

Commit message stolen from Id1a7c583894ac368bdcc61facc6f72300db320c7
Closes-Bug: #1392633
Change-Id: I61b0b6a21628d5629b5f80768e73ee44db05d1ce
Merge "Scality driver:use self.configuration instead of CONF"