http://libguestfs.org/ provides both utilities and libraries
to manipulate image files containing various operating systems.
It supports various image file formats and so will expand
the formats and guest types supported by openstack.
It does have extra overhead in that it starts a VM to
access the image. This has both advantages and disadvantages.
Also qemu-nbd is not supported on some systems like RHEL 6.
* nova/virt/disk/api.py (img_handlers): Add guestfs to the default
list of access methods to try, to act as a fallback.
* nova/virt/disk/guestfs.py: A new plugin class to provide support
for libguestfs mounting.
Note we use the guestmount utility, as a non root user,
so the user will need the ability to use fusermount, which
is often provided by being a member of the 'fuser' group.
In future we might use the guestfs python module to give
greater granularity of control over the image.
Change-Id: I2e22c9d149fff7a73cd8cebaa280d68d3fb9096c
a7e21b64b9