libxl: Add a test suite for libxl_domain_config generator

The libxl library allows a libxl_domain_config object to be serialized
from/to a JSON string. Use this to allow testing of the XML to
libxl_domain_config conversion process. Test XML is converted to
libxl_domain_config, which is then serialized to json. A json template
corresponding to the test XML is converted to a libxl_domain_config
object using libxl_domain_config_from_json(), and then serialized
back to json using libxl_domain_config_to_json(). The two json
docs are then compared.

Using libxl to convert the json template to a libxl_domain_config
object and then back to json provides a simple way to account for
any changes or additions to the json representation across Xen
releases.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
[update to v3.5.0-rc1, improve error reporting, use /bin/true emulator]
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

m4/virt-driver-libxl.m4

@@ -80,6 +80,10 @@ AC_DEFUN([LIBVIRT_DRIVER_CHECK_LIBXL], [
       LIBXL_LIBS="$LIBXL_LIBS -lxenctrl"
     ])
 
+    dnl Check if libxl_domain_config_from_json is available for domXML to
+    dnl libxl_domain_config tests
+    LIBS="$LIBS -lxenlight -lxenctrl"
+    AC_CHECK_FUNCS([libxl_domain_config_from_json])
     CFLAGS="$old_CFLAGS"
     LIBS="$old_LIBS"
   fi