IVGCVSW-6611 ExNet prints inference time twice
IVGCVSW-6611 ExNet prints inference time twice

 * Created individual IRuntime sharedptr in ExecuteNetwork main() each time
   MainImpl() is called. Prevents additional runtime being created when the
   delegate is used.

Signed-off-by: Cathal Corbett <698efcb37030a7415e79e4cf379eb09f757d0834@arm.com>
Change-Id: Ia4b508fbf2bbd25467c6235fed2f05662a7aecc0

ARM-software/armnn,ARM-software/armnn,ARM-software/armnn