core: [ExternalTasks] When adding new step...

[ExternalTasks] When adding new step, state is always STARTED

Removing the state parameter when adding a new step, it is really set
implicitly to STARTED.

Change-Id: I16ad3d25d527360b8cfb9eaefc66569700a3e4b0
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=988087
Signed-off-by: Eli Mesika <emesika@redhat.com>