If qemu-nbd is not present at the host system, only accept raw images
as input media. This is a workaround for ancient systems like CentOS 6.x
where the nbd module is not compiled in the default kernel and the qemu
package does not include the qemu-nbd executable.

Older versions of qemu-img do not accept a '--output json' option

If you are a regular user, some root commands like modprobe may not be
in your path.

Only use the device mapper when snapshotting block devices. If the
input media is a regular file, then create a qcow2 image and define
the original media as backing_file.

Use qemu-nbd to export a QEMU image as raw where needed

This used to be a class in the util module, but since this is only used
on the Image, it suits better there.

When snapshotting make sure that the size of the underlying block
device is equal to the input media's virtual size. If the input media
is not raw, the QEMU image driver may grow the underlying image. The
block device should be big enough to allow this kind of operations.

When the user picks a directory that contains VirtIO drivers, show him
the version of the discovered drivers in the confirmation box.

According to the decision of the GRNET Board of Directors,
switch license to GPLv3.

This commit will be propagated to the release
and master branches based on git flow, and the next
release will be licensed as GPLv3.

It used to be a function in util module

The machine hardware name fetched by `uname -m' should have been
stripped, and a --enable-kvm option should be added if the returned
executable was qemu-system-<arch>

On some systems it is kvm, on some others it is qemu-system-x86_64. On
32bit PC it is qemu-system-i386

This function is used to check if a specified libguestfs version is
smaller, greater or equal to the installed one

 * Prefix all private methods with _
 * Write missing docstrings
 * Move all public methods above the private ones
 * Add module docstrings where missing
 * Define source code encodings on all modules

The cow file when creating images or the temporary image file when
bundling the host system may be large. Allow the user to overwrite
the directory under which those files get created.

Add a new try_fail_repeat function that wraps cleanup system commands
and retries them if they fail. There are cases where commands like
dmsetup, umount and losetup -d may fail with device is busy. In most
of the cases, sleeping for halve a second and retrying does the job.

PBS has now bocome sh.

All image-creator components now output messages using an instance
of one of the output classes.

Also merge data_cleanup tasks with syspreps and did a major cleanup

All printing had to be reordered and now it is done from a central point.

The package is buggy and we can use pbs to do the same thing.