Introduce a parser/formatter for the xl config format.  Since the
deprecation of xm/xend, the VM config file format has diverged as
new features are added to libxl.  This patch adds support for parsing
and formating the xl config format.  It supports the existing xm config
format, plus adds support for spice graphics and xl disk config syntax.

Disk config is specified a bit differently in xl as compared to xm.  In
xl, disk config consists of comma-separated positional parameters and
keyword/value pairs separated by commas. Positional parameters are
specified as follows

   target, format, vdev, access

Supported keys for key=value options are

  devtype, backendtype

The positional paramters can also be specified in key/value form.  For
example the following xl disk config are equivalent

    /dev/vg/guest-volume,,hda
    /dev/vg/guest-volume,raw,hda,rw
    format=raw, vdev=hda, access=rw, target=/dev/vg/guest-volume

See $xen_sources/docs/misc/xl-disk-configuration.txt for more details.

xl disk config is parsed with the help of xlu_disk_parse() from
libxlutil, libxl's utility library.  Although the library exists
in all Xen versions supported by the libxl virt driver, only
recently has the corresponding header file been included.  A check
for the header is done in configure.ac.  If not found, xlu_disk_parse()
is declared externally.
Signed-off-by: NKiarie Kahurani <davidkiarie4@gmail.com>
Signed-off-by: NJim Fehlig <jfehlig@suse.com>