cubicweb #2535177 update Pyro documentation [deprecated]

The information in http://docs.cubicweb.org/admin/pyro.html needs to be updated,the example code:

cnx = dbapi.connect(database='instance-id', user='admin', password='admin')
should be change for:
cnx = dbapi.connect(database='instance-id', login='admin', password='admin')
other way the user will get an error like:
cubicweb._exceptions.AuthenticationError: authentication failed with all sources
because "login" must be used instead of "user".
* Other thing that looks like needs to be change is pyro the command:
pyro-nsd -x -p 6969
throws an error about -x not known option for Pyro4-4.11.

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