We use a non trivial image now (the registry's image in fact) and then
push with 4 processes at a time every time we push to the test registry.
The idea here is we're generating concurrency in the system that should
trip over the bugs that we are finding if they still exist.
Change-Id: I4f03132fa0fad6f40806030b14d429d29036a42f
8dfb9dc968