Make bootstrap arch match what we use for flavors

Previously the nova.conf in the bootstrap image would could get a
mismatch cpu_arch from the flavor extra specs used elsewhere in
TOCI. This change updates our extra specs so that we make extra
specs match (should all be amd64 when using 64bit).

Change-Id: Icb0d5ec2dd809884a16f8aaaa2954b78fac6ea96
Merge "Make bootstrap arch match what we use for flavors"