Move libvirt flags to libvirt group (cont.)

Following Michael's progress on blueprint libvirt-opts-group:

* Rename libvirt_type virt_type and move to libvirt group.
* Rename libvirt_uri conn_uri and move to libvirt group.

Move to libvirt group:

* libvirt_inject_password
* libvirt_inject_key
* libvirt_inject_partition
* libvirt_vif_driver
* libvirt_volume_drivers
* libvirt_disk_prefix
* libvirt_wait_soft_reboot_seconds
* libvirt_non_blocking
* libvirt_cpu_mode
* libvirt_cpu_model
* libvirt_snapshots_directory

Move libvirt_nonblocking to libvirt group and rename to
libvirt_non_blocking, correcting typo. Changes will be picked
up in output next time docs autoconfig is run.

Change-Id: Idbaa7d6c7ab3c4c2df56d0ad995214902fe6c115
Closes-Bug: #1253812
Merge "Move libvirt flags to libvirt group (cont.)"