restapi: Allow both "type" and "data"

The "type" and "data" elements used when importing a VM from a
configuration are both allowed and needed, but they are specified as a
XML schema "choice" instead of a "sequence". This patch fixes that.

Change-Id: I6d67b5b14b908c503c1e7d7fffb2a303cc026557
Bug-Url: https://bugzilla.redhat.com/1069522
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>