[multi-sources-removal] Turn ConnectionsSet into simpler ConnectionWrapper also, SqliteConnectionWrapper becomes a subclass. This is allowed since now ConnectionsSet responsability has been reduced to handling the system source only. This changeset also: * drops useless cnxset_set / check_connection api * deprecates former .source / .connection / container api but it renames neither the session's cnxset attribute, nor the related repository method. Related to #2919300

from logilab.common.shellutils import generate_password
from cubicweb.server.utils import crypt_password

for user in rql('CWUser U WHERE U cw_source S, S name "system", U upassword P, U login L').entities():
    salt = user.upassword.getvalue()
    if crypt_password('', salt) == salt:
        passwd = generate_password()
        print 'setting random password for user %s' % user.login
        user.set_attributes(upassword=passwd)

commit()