Support using Ibis connection in RemoteOmnisci

[pearu]

When having a live ibis connection con, RBC RemoteOmnisci should use the same connection. Workaround:

omnisci = RemoteOmnisci(host=con.host, port=con.port, dbname=con.db_name)
omnisci._session_id = con.session_id

Implement:

omnisci = RemoteOmnisci(connection=con)

or similar API