libxl: Allow libxl to find pygrub binary.

Specifying an explicit path to pygrub (e.g. BINDIR "/pygrub") only works if
Xen and libvirt happen to be installed to the same prefix. A more flexible
approach is to simply specify "pygrub" which will cause libxl to use the
correct path which it knows (since it is built with the same prefix as pygrub).

This is particular problematic in the Debian packaging, since the Debian Xen
package relocates pygrub into a libexec dir, however I think this change makes
sense upstream.
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NJim Fehlig <jfehlig@suse.com>

src/libxl/libxl_conf.h

@@ -53,7 +53,7 @@
 # define LIBXL_LIB_DIR LOCALSTATEDIR "/lib/libvirt/libxl"
 # define LIBXL_SAVE_DIR LIBXL_LIB_DIR "/save"
 # define LIBXL_DUMP_DIR LIBXL_LIB_DIR "/dump"
-# define LIBXL_BOOTLOADER_PATH BINDIR "/pygrub"
+# define LIBXL_BOOTLOADER_PATH "pygrub"
 
 /* libxl interface for setting VCPU affinity changed in 4.5. In fact, a new
  * parameter has been added, representative of 'VCPU soft affinity'. If one