[server] Separate repository bootstrap from initialization
Thus we now call 'bootstrap' here and there explicitly and remove call of this
method in Repository.__init__(). This way instantiation of a Repository does
not *implicitly* triggers the "bootstrap" step, which is arguably not a
trivial thing and thus deserves to be independent.
In __init__, set 'shutting_down' attribute to None and then to False in
bootstrap as a mean to indicate that, when initialized, a repository is
neither shutting down nor started (not sure where this is used though).
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances