xenstore: add explicit memory context parameter to get_parent()

xenstore: add explicit memory context parameter to get_parent()

Add a parameter to xenstored get_parent() function to explicitly
specify the memory context to be used for allocations. This will make
it easier to avoid memory leaks by using a context which is freed
soon.

When available use a temporary context when calling get_parent(),
otherwise mimic the old behavior by calling get_parent() with the same
argument for both parameters.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>