Add logic to parse complex labels that contain dependencies separated with +'s.

This CL creates a site_ implementation for the scheduling utility that allows
us to parse labels that may have nested dependencies in them.  These nested
dependencies are separated with a DELIMITER (currently +) that allows a Job
to create jobs with depenedent labels by using label1+label2...+labelN etc.

BUG=chromium-os:22179
TEST=This unittest.  Excerise both conditionals see metahost_scheduler.

Change-Id: I4174bb2c7547c4f684d9eca5d01a870bfdc8969c
Reviewed-on: https://gerrit.chromium.org/gerrit/13143
Commit-Ready: Chris Sosa <sosa@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
2 files changed