Set branch.autosetuprebase to always when setting up new deployment

People like doing `git pull` because it's easy to type, but this
creates opaque merge commits when there's livehacks. This will
make git pull do a rebase by default when pulling.

While we're here, say something more helpful than "Error running git"

Change-Id: Idf23df01d03e057588fd9c5db3edc3df9ff2bbff