Rhubarbe

* the various main() functions that create a Scheduler object
were written at a time where the default was critical=False
restore this default behaviour here; some of these tools are
used in the nightly check done on R2lab

* flush a couple ops-oriented changes
* make sure accountsmanager is always running even in case of temporary glitch
* 'make infra' to also restart monitorphones
* clean up of setup.py

* bugfix in accountsmanager:
* consider only login entries that have a valid homedir
* protect replace_file_with_string against non-existing dir

* new access policy; we now have three of them which are
* `open`: all slices can enter at any time
* `leased` : only the slice that currently has the lease can enter
(formerly known as `closed`)
* `closed` : no slice can enter at any time
* use setuptools instead of distutils for setup.py
* no more runner script bin/rhubarbe, see rhubarbe/__main__.py instead
* `/etc/rhubarbe/rhubarbe.conf` no longer used, ships as a resource (under config/)
* new subcommand template to expose the json templates
instead of storing them in `/etc/rhubarbe`

* emergency fix for a few lingering calls to orchestrate(timeout=timeout)
* configurable access policy; only 'open' and 'closed' supported for now
* for preplabs: configurable list of accounts that do not need a lease;
this extends the previously hard-wired 'root' account, and by default
it comes with 'root' and 'guest'
* thoroughly made pylint-friendly

* another bugfix; rhubarbe leases --check displayed current login name as None