restapi: Fix parameters of add DataCenter

The "local" property of the data center is mandatory, and the version
numbers are optional.

Change-Id: I5db741f4a6d9d479feaf5a51a745e0d0190f841b
Bug-Url: https://bugzilla.redhat.com/1104085
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>