A bunch of plab interface updates that I've worked on over the last while.
Most significant is the revamped renewal code that tries to push the leases
out to the policy defined maximum of two months during each iteration through
the plabrenewd daemon loop.

- added python lib code to get SiteVars
- Fixed up comments to reflect current code operation
- revamped renewal code (again)
  - changed all times to UTC for consistency
  - removed node-level renew invocation in favor of slice-level
    - if backend module requires node-level renewals, it must handle them
      itself in the slice-level function
    - better reporting
- set admin bit if creating svc slice
  - other updates to ensure admin bit is preserved
- update rootball handling function naming
- updated tryXmlRpcCmd() to accept two new sets of strings, and a callback
  function.  The strings represent Faults that either 1) indicate success,
  or 2) indicate failure.  The callback is another optional error handling
  method, allowing the caller to...