build: limit --all to 10 apps at a time
This needed now because the buildserver is hanging so often, that we are often going a week or more without any builds published. Perhaps this is only temporary, or maybe we will want to flush this feature out more as a standard thing. But we really need it for now to at least get some builds out on a daily basis. Since the website deploy is also triggered by this cycle, making the build finish more often means the website will be published more often.