Fix several Run-related race conditions [2/4]

Fix a few races around Runs:
* Only one caller at a time should mess with the Run table.
  Since we are using a database that has the right capabilities,
  throw a table lock into all top-level transactions that mess with
  the Runs table in any way.
* Refactor Run.enqueue and Run.run! to make the former a
  special-purpose function used to bypass some of the one-job-per-node
  rules, and let Run.run! handle all the usual use cases.
* Refactor the jigs to let Run.run! precalculate what any given jig
  will need for a run and then pass that in instead of letting the run
  use whatever state happens to be lying around when delayed_jobs gets
  around to doing its thing.  This helps keep parallel Jig runs
  interconsistent.


 .../models/barclamp_provisioner/dhcp_database.rb   | 70 ++++++++++++----------
 1 file changed, 39 insertions(+), 31 deletions(-)

Crowbar-Pull-ID: 7e4d4af3d6449b9d69d65e99a3e4e9c72ba47979

Crowbar-Release: development