Add an --output-dir cli arg to be used alongside --config-download. The
arg controls where the downloaded ansible playbooks and log files will
be stored on the local filesystem.
The path must be writeable by the current user and mistral user, so it
will typically need to be pre-created manually with the correct
permissions.
Depends-On: I89b17d0c4f035705fd5230caad06d331fd5b5e76
implements: blueprint ansible-config-download
Change-Id: Iff7a1b211a545f1227b9e13e304b858128fb855b
4fa13a9e88