Incorrect error message in Pure cinder driver

[Simon Dodsley]

There is an error message in pure.py on line 484 that references the PureISCSIDriver. This needs to be more generic as there is a fibre channel driver for Pure which can also produce this error message.

Error is in

reason=_("PureISCSIDriver manage_existing cannot manage a "
                         "volume connected to hosts. Please disconnect the "
                         "volume from existing hosts before importing."))

Change to something more generic, or define which driver is being used and be specific.