Disable libvirt driver file injection by default

DocImpact: This changes the default for file injection and key
injection with the libvirt driver. Most people should not need file
injection (the metadata server and/or config drive are more robust,
better options).

UpgradeImpact

blueprint disable-file-injection-by-default

Change-Id: Icff1304fc816acc843f8962727aef8bbbc7bbaa3
Co-Authored-By: Russell Bryant <rbryant@redhat.com>
Co-Authored-By: Steve Kowalik <steven@wedontsleep.org>
Merge "Disable libvirt driver file injection by default"