/distribution/beaker/setup: don't run builds in parallel
    
    When run in standalone mode (server and lab controller) the two code
    paths are run in parallel, in separate background shells. When both code
    paths attempt to do a git build they trample over each other in weird
    ways.
    
    Change-Id: Id0f71829cb19cf23503265c06bdb2f011ea1dfad