[cwconfig] Add "pyramid" config type to MCOMPAT dict
I don't know what this is for exactly, but the accept_mode method below
queries this dict with the configuration type name. And if the latter is
"pyramid", it crashes since there's no key in MCOMPAT dict. So add one with
the same value as "all-in-one". This code is called during "upgrade"
migration in particular.
[pyramid] Avoid shutting down the repository at exit if it's already shutting down
For install `cubicweb-ctl pyramid` command will explicitly call
`repo.shutdown()` so the atexit hook is redundant. Prevent the latter to be
executed when the repository is already shutting down (otherwise one gets an
assertion error).