Add support for the build manager

This adds a number of `pe:jenkins:managed_*` tasks to interact with
the build manager. These jobs are wrappers around the non-managed
tasks of similar name which initialize the build manager for a new
build, and then call the underlying task with some extra parameters
set in order to ensure the various packaging runs know they are
managed.

It also modifies the `pl:deb`, `pl:mock`, and `pe:local_sles` tasks so
that they will check in to the build manager on completion if a
managed build is running.

The wrapper methods needed to enable both managable build tasks and
`managed_*` wrappers are general-purpose and should also work for FOSS
or future PE platforms.