libxl: add feature flag to xenstore for XS_RESET_WATCHES

Tell guest about availibilty of xenstoreds XS_RESET_WATCHES function.
Guests can not issue this command unconditionally because some buggy
toolstacks (such as EC2) do not ignore unknown commands properly.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/xend/XendDomainInfo.py

@@ -1770,6 +1770,7 @@ class XendDomainInfo:
         f('store/port',       self.store_port)
         f('store/ring-ref',   self.store_mfn)
 
+        f('control/platform-feature-xs_reset_watches', True)
         if arch.type == "x86":
             f('control/platform-feature-multiprocessor-suspend', True)