cloud-init: don't use /tmp for config files

cloud-init: don't use /tmp for config files

Leaving files in /tmp was mostly useful for debugging
purposes initially. Also /tmp is a rather insecure option
for this for a final version, so use
/run/pve/cloudinit/$vmid, and move the file writing into
commit_cloudinit_disk() which now takes a hash mapping file
paths to contents, to not duplicate the temp-file logic for
the different citypes.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>