Add option to disable "d1" Swift device

Add option to disable "d1" Swift device

A default TripleO installation uses a local directory named "d1" to be
used by Swift. With SwiftRawDisks set it is highly unlikely that that an
operator wants to use this any longer, because it affects system
perforamce and might result in an overfilled the system disk. In this
case d1 should be no longer when building rings.

This patch makes it possible to disable the d1 device usage in the ring
building process by using a new option "SwiftUseLocalDir". This is set
by default to true, not changing the default behavior. If set to false,
the d1 device won't be used when building rings.

Closes-Bug: 1634051
Change-Id: Ia9ad38e3ffa533e170f4cedd0518d830e9b2fa69