core: Locate data source in a loop

The deployment of the data source usually finishes before the
application is started, but in some situations, for example with slow
DNS, it can finish after the application has started, thus we can't
assume that it has already been deployed.

Change-Id: I72c99c61d05e8a1619c7d1fb70af956d1050eb3a
Bug-Url: https://bugzilla.redhat.com/879904
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>