libxl: Fix uninitialized variable in libxl_create_stubdom

It is used for result domid from libxl__domain_make, but actually this
function have assert on an initial value.

This patch is intended for xen-4.1 only - 4.2 and later have reworked
this part of code already containing the fix.

Signed-off-by: Marek Marczykowski <marmarek@invisiblethingslab.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_dm.c

@@ -458,7 +458,7 @@ static int libxl_create_stubdom(libxl_ctx *ctx,
     libxl_domain_create_info c_info;
     libxl_domain_build_info b_info;
     libxl_domain_build_state state;
-    uint32_t domid;
+    uint32_t domid = 0;
     char **args;
     struct xs_permissions perm[2];
     xs_transaction_t t;